You haven't needed Bartab for on-demand tab loading for a while now, it's the "Don't load tabs until selected" setting on the Tabs page of preferences. Automatically unloading still requires an addon, though. I've got a serious tab habit as well (459 at the moment) and I'd recommend the Pano addon. It has tab/page title/url search that narrows the tab view to matches, drag & drop re-ordering (en masse), closing tabs directly from the list, tab group management, and visual indicators for whether a tab is loaded (nice when disconnected). It's nice when I'm cleaning out my old tabs to be able to put in ycombi, select all, and close them in one fell swoop. Heavy tab users probably want to turn on some of the optional features.
[Edit] Pano can also hibernate tabs or groups, so if that's the last thing you're using Bartab for it can replace that as well.
I just discovered that due to lack of time (if Google Translate is correct) Pano has been removed from the Firefox addons collection by the author and the github repository has been taken down. Since it's MPL 1.1/GPL 2.0/LGPL 2.1 according to the source I've posted a copy of what I believe is the last official release at https://www.dropbox.com/s/3yscqilam8gi8ut/pano%40teramako.gi... (please skim the code rather than trusting me).
[Edit] Pano can also hibernate tabs or groups, so if that's the last thing you're using Bartab for it can replace that as well.
http://teramako.github.io/Pano/index.html