Multiple issues as it's still a prototype.
From the press release, it looks like permanent magnets coupled to the spool shaft,= so a DC generator.
Such a system in a brand new purely DC system is fine, Frequency won't be an issue, no issues of THDi, THDv, TDD.
But if you have AC systems in the Aircraft, you will lose close to half your payload in 24 (12 min) pulse autotransformers, chokes and input line reactors to mitigate the harmonics and frequency requirements.
So if you do end with such a Stater/Generator, each and every device, relay, fuse, mission comp, harnesses, on MKI will need to replaced. , and if not, I dont think even removing the gearbox will give you the space to put the 12PAT enclosure in the same space. (Not to mention your 12PAT and the VFD's too will need cooling systems)
I don't know anything about the Rolls Royce generator, but they have managed to remove the IDG. I don't believe it's only a DC generator. You can generate AC also from this design.
I don't know if the Russians have planned something similar for AL-51. Anyway I don't see the IAF playing around with an engine that's clearly still a WIP. So even if the AL-51 ends up with an IDG, the Russians won't be able to introduce it on any other engine until it finishes development, never mind the fact that it may be impossible as well.
Anyway the point is, only 117S and 117 can be possible templates for any new IDG design. At least both have the CSD+generator combo as is.
So 117S/117 tech on AL-31FP or bust.