Some responses to your questions, while Biff gets back to the keyboard.
R8 LXDE 64-bit to R9 LXDE 64-bit : Biff has indicated elsewhere in the forums that the rolling-upgrade process has been imperfect in development. Unless that has been resolved, you'd be taking a major risk with your data if you relied solely on an in-place upgrade. You really need an explicit release note from Biff on that.
The versions of applications in Ubuntu 14.10 repos might be upgrades of the underlying app and they might be different because of major changes in Ubuntu itself between your 13.10 and current 14.10. If there's a list of dependencies, it doesn't sound trivial. Are you brave enough to compile your own copy ? Ubuntu forums are traditionally helpful places for such advice.
As for Debian stable/testing, is this what you have in mind ?
https://we.riseup.net/debian/installing-testing-packages-on-stable Quote from blog on the LXDE website Nov2014: LXDE is still actively developed and maintained <cuts> and as long as gtk+ 2 is in use, I believe that they’ll keep working on it. We even got some patches for gtk+ 3 recently. Yes, gtk+ 3. This does not mean that LXDE is going to use gkt+ 3, but it’s a clear indicator that LXDE is not dead. End quote.
As I understand it, some LXDE components haven't converted to LXQt (yet or ever ??); also LXDE has recently bumped its version number to 0.99 in anticipation of ver 1.0. Whether LXQt is ready to roll is less clear. Only Biff can tell you what decision he has made, but you could check the current news on the LXDE/LXQt websites and take a guess if you want.
.
