An excellent summary. Here are some thoughts.
Randomly block out different techs each game or not?
As previously argued, I think 'no' on this one, but could be convinced; I simply don't see a positive reward for this.
Many categories (10+) or fewer (6-8 )?
I view this question less as 'many or few' and more as 'specific or broad' - that is, HoI-style specific categories would give us, for example:
Corvettes & Destroyers (Light Capital Ships)
Cruisers (Medium Capital Ships)
Battleships and Carriers (Large Capital Ships)
Land Warfare (Infantry/Tanks)
Military Infrastructure (Shipyards, Missile bases)
Civil Infrastructure (Banks, Govt.)
..and so on. In this sense, the 'categories' are to the individual techs as the theories are to their applications; they are fairly specific 'parents' to which everything belongs. Whereas a MOO2 style, broad category list such as:
with one or two others -- that is really the choice. We could choose specific categories and still only have 6 or 7, or we could have 14 or 15. This number won't be finalized for quite some time, I suspect, but that's the decision I'm trying to get out of these threads.
Will it be possible to develop applications without knowing the theory, if all the prerequisites have been met, maybe at some kind of penalty?
I could be convinced about having an OR pre-requisite, but I think we sould establish a system and then play by it; offering 'ways around' the rules is tricky both in that it's an added layer of rules for the human player to remember, and its difficult for the AI to adapt to those rules.
Should we have techs that reduce the cost or time of research generally (or for particular categories). ?
I should say yes on both; which categories exactly and by how much we would have to balance later.
Should developing related (but not prerequisite) techs reduce the cost /time of developing a tech?
No. With a large tech tree, this would get ungainly as you would have to program in every tech to which the first tech is 'related' to; people would argue relationships where none should be and vice versa; all in return for which we are breaking the 'could not be operated by a human in a boardgame' rule for marginal returns.
Do we want to repeat the outline of the tech tree to extend the research game?
I'm not sure I understand this; if it's 'should the tree be visible,' then I'd say yes.
Should we have separate practical and doctrine categories a la HOI, or merge them together? (is this important?)
This is fairly HoI-specific and generally relates to the HoI concept of 'organization' in battle. I don't think it applies to us.
Should we try to hardwire choices with race bonuses to particular techs, or try and make it dependant only on strategic position.
HoI grants bonuses to categories based on the ministers you have in your government. Specific techs could be tricky as an easily mod-able tech tree could change techs around and render whole races inoperable. I would say, at least, allow bonuses to categories, and keep our options open for bonues to specific techs. But right now I can't think of a compelling reason why we would need to.
Do we want to achieve multiple paths by balancing all techs perfectly, or by deliberately introducing several 'prefered paths' or tech families?
I'm not sure I understand this. I think each race and/or each starting strategic position should have preferred paths, but several of them.
How can we produce genuinely alternative gameplay styles and support this with the tech system?
See previous posts.
How do we do this whilst keeping things relatively simple and fun?
Two rules of thumb: KISS and Steal, Steal, Steal!