They haven't ceased giving the 1.4 exam yet - in fact, they just recently stopped allowing folks to take the 1.2 exam. It's going to be a while, I believe, before they have some kind of cut-off for 1.4, so you're safe planning for it for some time to come.
I'm not sure all that many with 1.4 are going to upgrade to 1.5 - it's honestly just as easy to wait for the next version and do it then. (I know I did upgrade mine from 1.2 to 5, but I probably won't upgrade again - at least not unless it's through a Beta exam - until the version after next.) But others might be able to better speak to that.
And finally, yes, you'd be qualified to take the SCJD 5 exam with an SCJP 1.4 certification, as the only prerequisite is the holding of a valid SCJP cert, not a requirement for the current version.
Hope this helps!
Theodore Jonathan Casser
SCJP/SCSNI/SCBCD/SCWCD/SCDJWS/SCMAD/SCEA/MCTS/MCPD... and so many more letters than you can shake a stick at!