DI2 came out in 2001. How many years do you think this 'fad' will last?

How's market adoption?

A question with a question that's easy enough to google? Come on.

https://www.prnewswire.com/news-releases/bicycle-gearbox-sys...

Still growing at a nice rate and every single pro team has been using it for years now.

All I see now around where I live, which is heavily bike centric, are e-bikes...

I’m not sure that is the correct metric to look at. As it is a very very high end product.

Precisely. If it was a truly innovative, no-brainer upgrade like dropper seatsposts, you would find almost one every recent-ish bike. I have seen one (1) live so far. And it was a ultra high end road bike.

For the same reason, what the pros do on their rigs is no concern for the 99.9% of mountain bikers.

I wouldn't bring anything I can't repair or troubleshoot directly out in the mountains, let alone anything that can discharge and not work anymore.

I have three bikes with electronic shifting in my basement. None are “ultra high end road bikes”.

Shimano also brought electronic to their 105 line and SRAM has it on Rival. Neither is high end, never mind ultra high end. I’m not a MTBer so I’m not aware of how that market is, but electronic shifting is definitely prevalent in road, gravel and cross.

If you’re talking DuraAce/Red then yes. Otherwise it does not truly qualify as “very very high end” or even “high end“ for Rival/105.