Man, I wish I could get to where you are! You mention a Mesa 4x12, so to run with that example I have 8 IRs loaded that are all Mesa 4x12s. They have names like "110 412 C MES-ST V70 OH1F" which tells me the IR slot number (for file management purposes), that the cab is a 4x12 closed back cab, specifically it is a Mesa Standard Slant cab, it is loaded with 70w Vintage 30s, and is Ownhammers OH1F mic mix. The other 7 are different cabs, different speakers, different mic mixes, and I use different ones for different sounds with different guitars. Add to that the fact that there are also Marshall, Bogner and Orange 4x12s loaded, and that in addition to that there is a similar variety of 10/12s, 1x12s, 2x12s and 4x10s, and yes, all of those pieces of information are necessary to find the one I'm looking for. "Mesa412" won't cut it.
When auditioning a new IR library, loading them directly inevitably results in the end of the original filename being truncated, and in a batch of similar IRs it is the end part that is unique. So if I want to know which ones I like when auditioning them, I have to change the names before loading them. Which gets cumbersome when you're checking out a lot of stuff.
In short, if you're only using a small handful of IRs, the current filename length restriction is a non-issue. If you like an assortment, it's a major stumbling block. It may be a limitation of the filing system as you point out, I can't know.