I think the C100 looks like a cool mic, and the sample recordings sound like it could be useful for sure. One thing that might keep some old timers from warming up to the C100 is that the SDC element is an electret, which was initially associated with low cost home and prosumer mics. And electrets are, at least on paper, capable of losing the capsule polarization over time. That said, Sony has had good experience with a number of electrets before; the ECM 377 in particular was not bad sounding. And there are other modern electrets like the KSM32, which are good utility general purpose mics. If that’s where your instinct tells you to go, why not. Probably won’t suck, and it is a whole world of new sounds and approaches to be had.
On another note...
If you plug in a U87ai next to vintage 87, the AI is going to have more level and tap out the headroom of the preamp faster. The other thing going on is that the vintage 87 and the AI are usually strapped for different output impedanxes by default - vintage often at 50 ohm, AI at 200 ohm stock. Some preamps and boards will yield more difference with that than others, but you can adjust the way the output transformer is strapped. It is really pretty difficult to overload the internal electronics of the AI unless you go for a brutal kick or snare drum position, so that is unlikely.
The 87 and 414 are almost inherently linked to the history of recorded music in a way that few other mics are...part of the evolution of Neumann’s line from 47, 49, 67, 77, 87, 87ai and then AKG’s C12, C12a, 412, and 414. It’s hard for anything to come along and change what people associate as being the tones of classic hits. So that is a unique slot even if other mics come along and have objectively desirable qualities.
There are definitely mics I prefer to the 87AI but the fact remains that if you’re working with someone and they are wanting to layer up some overdubs, do a bit of this a bit of that, and you are going by the seat of your pants... it is a *great* choice. If the results sound wrong it wasn’t the mic, and if anything the 87ai “sounds like a record”.