So, reading around the forum a bit I discover I'm not the only one who thinks the Tech Tree display is badly in need of overhaul.
It's beginning to appear to me that the tech-tree itself doesn't meet the FO "kiss" principle, and begins to stray perilously close to "micromanagement".

Particularly for "theory" techs: why? Looks like they are only there to fulfill simulationist urges... and maybe because it's "traditional" in the MoO/Civ/etc genre...? I mean,
really:
why? Why must the user click on something just to later click on what they want? Whatever tech(s) depend on the dependency: just click 'em directly, let 'em take a bit longer to develop.
I know that one can already DO that, click on an advanced tech and get all the pre-req's auto-queued.
So why make them separate click'ables???!? Eliminate
all the Theory tech's. If needed/desired, SitRep those intermediate/theory techs with something like "The Directorate of Science reports a breakthrough in Gravitonics. They believe we'll be able to achieve Singularity Generation in <N> turns. Also, the Directorate report several promising new technologies arising from Gravitonics: Compressed-energy ship-hulls, null-g architecture, and supply-chain efficiencies."
I don't actually object to having theory tech's in a 4X game... but they don't IMHO seem to "fit" with the feel or the philosophy of FO, as I understand it. They belong in a different -- also fun, but more simulationist-oriented -- 4X game.
It's possible that this issue is more UI than anything else... not really sure...
The only notable "simplification" to the UI that I've been able to think of, so far, is a "collapse branch/branchpoint" function; that is, a whole "branch" of the tech-tree (or all techs subsequent/dependent to a given tech) gets collapsed to a big thick line; the difference vs. the hide/filter effect would be that dependencies into (and out of) the tree/branch would still appear in approximately-correct places (maybe via faded-out lines?), letting the user know of the inter-dependencies. Ideally, IMO, there'd be an icon such as "

" where one could hover/click, to find out what visually-collapsed tech is needed/available via the indicated dependency into or out of the branch. The idea is to preserve the high-level / strategic overview effect of the branch still being there, but hide all the detail so it doesn't distract.
I suppose something similar might be done by fading-out a tree/branch, rather than "collapsing" it; or doing some sort of minimize (shrink to small icons) ... ?
I suppose, with the code for such display on-hand, one could fade-out or minimize the "theory" techs that I ranted about...