Well the beauty of this idea is that you could use the achievement based tech side of the existing tech trees to expand the tech trees in a new and fun way while still retaining the feel and flavor of the original game. Also, the complexity wouldn't be overwhelming to new players, as the "prerequisite achievement" would always be event based and clearly labelled on any new tech.
In essence, making the old feel new, and adding another tactical element to the game as well.
currently, prerequisites tech's are just passive money dumps that, yes you do make an economic trade off for, but they are ALWAYS there to be made. This idea allows for tech advances that are event based which allows for players to have an effect on what a person can and cannot research. Lab destruction does this to some extent, but having in addition a "technology starvation" tactical plan would be an interesting addition to sins. Naturally the benefits of the difficulty of some of these in game events would have to be matched with the relative ease to create the event. the ice planet colonization would be a relatively easy one that might be a prerequisite to start a chain of tech that would ultimately lead to a new racial weapon system that kicks butt(which your opponent could take measures to prevent you from achieving the prerequisites if they were diligent). Use people to balance people, and save the designers a headache.
This could also make the game more engaging to single players, as they will have more little things to achieve and interact with in the game environment.
As it stands tech is an integral part of the game, but no more then an economic money dump. I'm not disrespecting the beauty at which this economic tradeoff has been orchestrated by the devs, merely the limitations of the current system.
Also, the devs currently use the logistics slots to create a trade off between structures in the grav well. This would free their development arms up and allow for tactical teching up, destruction of labs, AND a great excuse to add more planets with variable logistics slots in the game, making them not quite such a game maker/breaker.
Also, achievement based tech's could be prerequisites to awesome normal money dump tech's, or lead ins to other achievement based techs. In this way you could have an ENTIRELY different play style strategy that would be a viable path for victory.
In fact i'll go into detail into how you could orchestrate this into the game.
Put a flashing symbol next to a researched tech that indicates that an achievement is possible that is associated with that tech. the player, having researched it will click on tech (the fun of discovery!) which will open to the achievement specifics, what it might lead too and other pertinent information. The developers can increase the tech's in the game greatly with less of a worry because they would be dealing with something that is entirely preventable player side.
Simplified, you would research a tech, see shiny thing and click on tech, and then read what shiny thing means, and then do shiny thing to get potential awesome.
achievements such as "kill 50 enemy combat ships" to achieve a prerequisite for a sweet weapon upgrade tech would be pretty awesome, in my opinion. After all, the guy didn't have to let you rape his fleet, he could have ran! It would add a lot to the game 
