Di2 (and SRAM's equivalent AXS) has been getting aggressively trickled down the groupset line and the price has been dropping precipitously. It's a bit obscured by the ongoing supply chain issues, though.
Electronic shifting will become a standard, or at least a common option, on mid-range 105/Rival bikes ($2-4k) within the next few years most likely. The same way hydraulic disc brakes have trickled down over the past several years.
I still ride mechanical myself, but have friends with electronic shifting and they rave about it. It's nearly zero maintenance because it's self-adjusting. Just lube it and clean it, and replace the chain every few thousand miles.
Even though electronic shifting may be "better" I still find a beautiful simplicity in the all-mechanical nature of a bicycle.