Connector standards are one bit but the bikes vary wildly because they use different battery arrays - 36v (42v charge) and 48v (50+v charge) both are common.
The connector side is easy - XLR would work, XT60 would work but you'd need to ensure that all the bikes could accept a wide input voltage range or you'd need lose a lot of efficiency. If you just shoved a MPPT input on the bikes with XT60 you'd be able to just plug it into the panels directly *and* plug your own panels in too