This idea crops up from time to time, and the whole thing boils down to "I want one, so they ought to make it and I don't want to hear any arguments!"
Two things are against it, one being the latch. There is always a gap (there has to be so the gun can be opened) and every time the gun is fired the latch tries to pull apart and batters itself. Titanium alloys are tough, but won't take that kind of thing any better than most steels.
Then there is the problem with cartridge length. Look at the old break tops and examine the way they work and it is evident that ejection will be a problem with long cartridges.
Of course, I already know the response - "I want one, so they ought to make it and I don't want to hear any arguments!"