Most ebikes sold use fairly generic ebike parts. Proprietary parts are more expensive to manufacture so they are typically on higher priced ebikes but the average price of a bike sold in the UK is only about £400 and that includes ebikes. However that data doesn't come from all retailers but does include independent bike shops or at least the wholesalers and bike brands that supply them.
https://www.amazon.co.uk/Best-Sellers-Electric-Bikes/zgbs/sports/469685031
Proprietary is normally an issue for higher cost bikes or ebikes and less of an issue with cheaper models.
I think its important to point out most European and US bike brands are not manufacturers and those that are often are more assemblers than manufacturers with key parts coming from Asia. Most ebikes come from Asia and those that don't typically have a very high percentage of Asian manufactured parts.
Even if I had the money there is zero chance I would buy a high end Porsche ebike, I'm not into high cost yet disposable products like that.
I can't see Porsche making much of a dent in the marketplace in fact especially here where people's incomes are likely to continue to fall as the interest payments on government debts increase and the government is forced to tax more to pay the interest. Disposable income is likely to fall considerably as it already has and this will continue. Porsche may carve out a significant chunk of the high end niche ebike market but that is still very few ebikes overall compared to the Asian manufacturers and such high cost models are difficult to use day to day without risk of theft.