i certainly hope stardock won't fall into the classic trap of obsoleting lower tiered troops, when higher tiers of research are reached. This makes for a dull, linear, and simple game. Research should expand your possibilities, not just make you stronger in different areas, although this could also be part of research.
I mean, give it a thought: whats more interesting:
research completed! you have reached chain mail. Now your armor is twice as strong as before. Next level: doctrine: heavyer armor. now your armor is thrice as strong.
OR
You have aquired the iron resource. new research possibilities: chain mail
Research completed! you have reached chain mail. You can now equip troops with the following:
Chain mail (+2 armor -1 move).
You can now use chain mail in your magic item creation.
You can now sell chain mail to other civs.
You can now research "armor piercing", pre req: bows&xbows
You can now research "plate mail"
Aquire "Coal" resource, will allow you to research "steel", "steel" unlocks superior armaments.
or something