Mixing and matching across eyepiece designs / manufacturers? Right now, I am considering moving from 1.25" eyepieces to 2". While I'm convinced of the quality of the premium eyepieces, it would take me years to afford a complete set and, if I go that route, I will necessarily pick them up piecemeal. Would I be wise to follow that route, knowing that in a few years time I'll have not wasted any money? 
Or would I be wiser to buy a complete set of design X, which have great price/performance ratios and slowly replacing them with premium eyepieces?
Or would I be wiser to buy a few of type Y for higher-power viewing, which are still pretty expensive, but not as expensive as the 100 degrees field-of-view eyepieces, but maybe just buy 1 of those for wide-angle viewing? 
Or another strategy? I like to look at everything, so ultimately I do want a pretty wide range of eyepieces. But I kind of hate that with my current mish-mash, I have a "lumpy distribution" in quality.
 A: Don't worry about mixing and matching, but do buy quality. After 54 years in the hobby, I find that telescopes come and go, but I keep good eyepieces just about forever. Pay attention to which of your present eyepieces you use the most, and buy a premium eyepiece of the same focal length. If you find you like a particular design, buy more of that design, though be aware that quality is not necessarily consistent across the whole range of a particular design. Each design has its own "sweet spot." Read reviews but try, if at all possible, particular eyepieces in your scope on your favourite targets.
I've found it better to own two or three excellent wide field eyepiece than a whole bunch of inexpensive ones. At present I do 95% of my observing with my main telescope, a Celestron 11-inch Schmidt-Cassegrain, with only three eyepieces: a University 40mm MK-70 (70x, 70° fov, gives the widest possible field of view in a 2" barrel), a Tele Vue Nagler 16mm (175x, 82° fov), and a Tele Vue Nagler 11mm (255x, 82° fov). Tele Vue Ethos weren't available when I was buying eyepieces; if I were starting over, that's mostly what I'd buy. They are just plain wonderful!
Don't worry too much about eyepieces being parfocal. You can buy parfocalizing rings to make them all similar.
A: Regarding your "lumpy" distribution of eyepiece quality: Think about which eyepieces do you use most of the time.  I recommend filling the low quality dips piecemeal with your desired type of premium eyepiece, first replacing the eyepiece you dislike but use often.  
Upgrade from the middle out.  The eyepieces of the extreme range are probably used the least.
Skip buying eyepiece sets that include sizes you'll use very little and that you'll want to sell (at a loss) in the near future.  This is especially true if you know you will want to replace these eyepieces with better in the near future.
Look for eyepieces that are parfocal with what you already own.  That is, they have the same focus point so you can switch quickly between your eyepieces when transitioning from finding to viewing an object.
A: Go ahead, mix and match. Get what you need from any manufacturer, as long as the price reflects the quality.
Now, just to make sure, because there's something not clear about your post (and if I misinterpreted it, then I beg your pardon and please ignore the rest):

Right now, I am considering moving from 1.25" eyepieces to 2". While I'm convinced of the quality of the premium eyepieces

Well, you could (and probably should) install a 2" focuser on your scope, if you don't have one already. But in terms of eyepieces, the 1.25" vs 2" distinction doesn't have much to do with quality.
There are many high quality 1.25" oculars, TeleVue comes to mind foremost. There are many 2" lemons out there, I won't name names. And of course there are many 1.25"/2" "dual" oculars of just about any quality level between great and awful.
A good eyepiece collection should probably contain some 2", some 1.25" and/or some "dual" 1.25"/2" lenses.
The reason you need 2" oculars is: when you go above a certain focal length (let's say 32 mm) then you need to increase the field stop beyond the size that can be housed in a 1.25" barrel, otherwise your field of view will be reduced. In other words, if you want both a long focal length and a reasonable field of view, you need a thick barrel.
If the focal length is short, this is not necessary. The TeleVue Ethos 3.7 mm goes just fine in a 1.25" barrel, and yet has an AFoV of 110 degrees and is a very high quality ocular (expensive too).
A: You call it a "Lumpy" distribution.  This is typical of most Amateur Astronomers!  We begin with the purchase of a telescope and mount. These typically come with either one or perhaps two different Eyepieces, (EPs). Some have gone on and purchased a "set" of EPs in a nice case. One telescope maker offered a set like this.  Unfortunately, while the "quality" of the glass wasn't bad, it offered many EPs that left one trying desperately to view through a soda straw.  One method is to go out to an Astronomy Club's Star Party, or a Group viewing session.  Ask to look at other EPs, and Telescope combinations. Going to a 2 inch system can prove to be costly if done all at once.  Over the last 10 to 12 years, I've improved my "stable" of glass.  My first purchase was a Pentax SMC XW 14mm.  It was a 1.25", and did not require any additional adapters.  However, they are NOT inexpensive! I happen to have multiple hobbies. Using another one, I horse traded some R/C equipment for Astronomy Items. This got me into a refractor, and several 2 inch EPs. I was the the new owner of a Williams Optics Megrez-II, 80mm, that was 2inch based.  Along with it came three EPs that just happened to be Televue Nagler Type 4s.  I ended up with a 12mm, 17mm, and a 22mm.  They have excellent AFOVs.  I've since acquired within the last two years, one of the then new Televue 13mm Ethos.  It takes time and patience.  Watch the "used" market for decently priced glass that we call "Primo"!  You find out what will fill YOUR needs and desires. Give it some time and looking at what others are using that show what YOU like!  I purchased a Televue Adapter that screws on to the visual back of my 8 inch SCT.  I then use the 2" diagonal from the WO refractor, and use 2 EPs, or with the diagonal's adapter, use 1.25 inch EPs.
