I do not have any problems with my single battery 21" SP. AND you do not have to use the SP feature. The mower rolls freely - no drag when not using the SP. I rarely use the SP. My wife and son do when they mow. Works great either way. So, go ahead and get one .
I would think that the thought at Ego is people would purchase the dual battery because they have a large lot and thus they would want SP. So, I would doubt a push model would be produced. Just my 2 cents.