I'm not sure you've thought the idea all the way through. It is a good idea.
However, to get similar and reliable functionality that we have now, we would need a legacy pack for each update that allows each update to function as an older version. Assets are not the only issue between releases. As SCP adds features (new tbms, table features to replace asset hacks, etc.), those are changed or removed in favor of the more modular design. HUD is good example of something table based that has changed several times over the last couple releases. These Legacy Packs would need to restore functionality to 3.6.10, 3.6.12, and eventually 2014 for older mods to receive the full benefit. And even then, how do you install something like that?
Perhaps you were only thinking of assets and not other types of version Legacy rollbacks. In that case, the tiles pack is already available... nothing else critical has been removed unless you really want that old Mentu model. (Actually, for upgraded models that are replaced with upgrades.. that may not be too far fetched.)
Something I haven't seen discussed yet is that even if we did change to a sole 'MediaVPs' install folder now. We have just about 4 years of mods that now rely on 'mediavps_3612' and 'mediavps_2014'. These are, arguably, the mods that most players will be playing and until the mod authors update them, we'll have the same issues as now.. just in reverse.
Also, I have continued to follow the thread that spurred this.. and I'm not convinced the guy is even following instructions correctly. It makes me wonder if this issue has only presented because of one loud user having issues where 40 quiet users are enjoying the game already.