The dilemma when talking to manus while making the rules is always the same...

a) listen to the 2-3 manus that are in the series at the moment to make them stay
or
b) listen more to those interested in joining (but then you need firm commitment at some point)

The manus already in the series are very likely to want as few changes as possible so that they have a development advantage and can re-use as much of their existing cars as possible. The manus interested in joining will likely want the opposite.