Right. With disc based emulation, there is a legal loophole where they can say the owner of the disc still has the license, but they take no responsibility for how reliably it will run.
Which therein lies another problem, compatibility.
There were two reasons Xbox went the emulation method they went previously:
1) legal issues as covered above
2) all games are not equal when it comes to emulation.
The bigger problem is that the more complex a game gets, the more hacks you have to deliver to successfully emulate it on a software level. There is no blanket "press x to emulate" method, you need a series of different configurations to run a series of different games. Some will work just fine, but the more custom the shaders used or push the original system, the more hooks will be needed to deploy.
So while you could in theory offer 100% emulation of lets say PSOne, you may not so easily be able to offer a resolution bump to everything as a uniform setting, because higher resolution actually breaks a LOT of PSOne games. Ps2 is much better, but again, it's more complex emulation.
People think that you just need more power to emulate a new console, when the truth is you need more power to emulate accurately, and sometimes... That's just not possible.
So, what will be more than likely, is you may get ps1/2/3/4 emulation at the software level, but it may not offer any enhancements over basic stuff.