If bethesda had actually cared enough, would they have been able to implement esl format for other games like New Vegas?

Don't expect anything from Bethesda about Fallout New Vegas.

what would be the point? Esm and Esp files work well enough, not to mention FNV's load order system is messy enough without Bethesda "sorry our update broke the game" Softworks screwing around with it.

Also, Fallout New Vegas doesn't have a console presence in the same sense as 4, so I can't see Bethesda putting much effort into updating it.

Ehhh.... maybe if they test it with user mods and it doesn't do anything quirky.

Edit:

And we also have merged patches via xedit so...

It's a hassle trying to merge mods.  Some people aren't bugged by it, but I'm trying to compile written lists of which mods go into which merge, it's a project in of itself. it's doable, but it shouldn't have even been necessary -- I don't have to merge on a heavily modded skyrim or Fallout 4.
I've got a merge category for various treak mods, freeside mods, a strip mods category, merged weapons,  a novac and primm and etc etc category of mods.  None of that would be necessary if the mod limit had been higher.

Edit: And I should have said, "Could Obsidian add .esl to New Vegas if they felt like it?" Meaning, both from a legal and technical standpoint. Perhaps New Vegas is absolutely incapable of using the mod-surpassing .esl anyway.
Bethesda certainly won't do it, I'm sure, even if it was as simple as flicking a light switch. NV's bugs are probably a benefit to them at this point (or simply irrelevant), with some people comparing the venerable NV highly to aspects of fallout 4.