Thought about this..
The ink type is different.. its a gel, it has different viscosity.
Also they are only 4 colour printers.
Sawgrass have an inkset they use for small fabric based prints "fabric maker"
So if they have a solution for fabric then it is achievable to turn one into dtg.
As stated above the issue you will run into, refillable cartridges? auto reset when cartridge is empty... etc etc
The thing i do like about the Ricoh print engine (SG series) is the auto head clean functions that run every few hours.
Doesn't waste a lot of ink either.
Played with them for years as dye sub printers.