I too have heard on good authority that AV is likely to replace FPTP within the next few decades. This is of great concern, as there are some serious problems with AV: see
this page.
Estimates show that the only party that would benefit from AV+ is the Liberal Democrats, as most voters would put them second (and of course they would be most likely to enter into a coalition with one of the other main parties).
TR sounds interesting; I may look into that further. The immediate problem I can see is that it may lead to coalitions, which entails the political parties choosing the government rather than the voters. I looked into the issue for an essay I wrote for my degree and there are serious problems with any system that results in coalitions - I think I wrote in more detail in another thread, but essentially it becomes extremely hard for voters to change the government, and there are many bizarre outcomes where parties can increase their share of the vote yet lose their place in government. Our current system is not perfect by any means, but I remain to be convinced that an alternate system could do better.