You can already buy research points with GP (granted it's a really crappy rate that should be updated, but...) and you get Alien Data Disks from your AP pulls.
By enabling someone to buy research points with credits takes away one major dynamic of the game. The choice between mineral production and research production. And before anyone says "well the research contract does that too..." keep in mind that the contract unlocks with only about 1/4 of the total research needed to completely finish all current research. There are currently only a small handful of people completely done with research and some of them have ship upkeeps of 20B+ and colonization/invasion costs even higher. To them, the research contract is just a secondary income source to help cover their exorbitant expenses. Once you finish all research, there is no other use for it until something more gets added. There will always be a need for credits.
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[20:40] Wredz: just hacked a massive extremely rich minting planet from someone.. thats the best planet i ever hacked
[20:43] DarthFlagitious: is it spearmint or peppermint?