New here, but made an account to add my voice to the suggestions page. I really like a lot of the ideas posted here, but I'm not quite sure i agree with a Guild system per se, but maybe adding certain Guild buildings that certainly open up different R&D options would be nice. I'm thinking a Masons Guild building, that opened up all kinds of advanced construction and also was able to turn stone into different types of rock at various rates. I imagine it would look like a tree of quality like this:
Stone > Cut Stone [Build Masonry to unlock more]> Reinforced stone > Granite [Convert 2 rock into 1 granite] > Cut Granite [Established Masonry to unlock] > Reinforced Granite.
After reaseraching to reinforced stone and granite, unlock a whole new tier of upgrades for every single building allowing you to upgrade them 3 more times with the new mats, and then a final upgrade after getting reinforced Granite fro all buildings.
Note: I'm only using Granite as a general term, as it's a fantasy game Vs corruprtion maybe name it something neat like LightStone, and it's magically imbued stone to fight against and protect from the Corruption. It also faintly glows so at night your city is lit up like a fantastical magical oasis.
Then of course an Arcanum. This would require an Essence Collector to function, and you can assign Arcanists to not only research new spells but to upgrade existing ones. Keeping in line with the above suggestion, the Arcanum can produce upgraded Crystals. I'm imagining:
Crystal> Crylithium [Build Arcanum to unlock] > Pure Crylithium > LightCrystal [Converts 2 crystal stores into 1 LightCrystal] [Established Arcanum to unlock] >BrightCrystal
This would unlock higher tiers of Defenses and essence collectors, as well as new buildings that could create magical equipment for your populace and maybe at the highest tier allow creation of a Portal Device allowing you to interconnect multiple setllements with a WayNetwork for fast travel between them
Then a Guild of Heroes. This would be cool if it took Essence to very slowly build up and attract powerful hero units that the player can control, and you could have Armsmasters who when assigned to the Heroes Guild train your hero and constantly feed it XP, and also researches a myriad of new abilities so that when the Hero hits certain level milestones you can custom build the hero you want. Limit every settlement to only a single hero unit, and as you upgrade the guild of heroes it increases number of armsmasters and levels him more effectively/researches higher tier abilities.
These are just a few of my personal ideas I've been chewing on since i picked up RtR, but this game would absolutely benefit from any form of R&D.