In $\Lambda\mathrm{CDM}$, structures form "bottom up" with larger structures forming later. Structures are generally speaking supported by the velocity dispersion of their constituent objects (e.g. elliptical galaxies are supported by velocity dispersion of stars while galaxy clusters are supported by velocity dispersion of galaxies)$^1$. More massive virialized structures require higher velocity dispersions to support them. What happens when the velocity dispersion required to support a structure becomes relativistic and eventually exceeds $c$? Does the structure simply fail to collapse? Collapse to a black hole? Something else?
It occurs to me that the $\Lambda$-driven exponential expansion that is currently thought to be getting under way in our universe might be rapid enough to cut off structure collapse at some scale, avoiding the scenario I described above. For the purposes of this question, let's assume for convenience a model where the Universe continues to expand with $\lim_{t\rightarrow\infty}\dot{a}(t)=0$.
$^1$ With the notable exception of systems where dissipation is important, allowing the formation of a rotationally supported disk.