Do you really have doubt this day isn't coming very soon? 2023 tops. Mercedes SUV are niche luxury. Tesla will only shed away price on the Y's due to declining battery prices, improved manufacturing with gigafactories, and their mission of reducing emissions by getting everyone into EV's.
I mean sometimes I think "who the hell needs a GLB AMG??" but it's one of the few SUVs of that size that seats 7 passengers and serves a need for families in certain EU and Asia markets.
Any given Mercedes SUV may be niche luxury but they cover many many niches with their lineup.
Literally the Model Y also. Not sure if this is the need you're referring to or something else. But Mercedes is far behind on EV's and not even close to Tesla. This switch is happening now, if you haven't noticed all the SUV PHEV, ID.4 launch, and Toyota BZ4x announcement. Once the majority of developed nations aren't using much gasoline, taxes will be raised and Mercedes lack of EV will be critical. I mean they are almost dead last behind Tesla, VW, BMW, Nissan, Toyota, Honda, Ford, GM, etc.
Tesla bundles its sales with the Model 3 (bad sign) & 3rd party data suggests they sold 3k in Q4:20 with negative trending.
I agree EVs are the future, I think Tesla was a major innovator in the space, but has stagnated recently and the blind faith in Musk / Tesla is ultimately bad for the cutover