read lot of comment that what if Johor merged with SIngapore. IMO, It is better to remain their own sovereign rights than merge together. Maybe a model similar to EU will be better.
SG can co-operate with them to boost their economic. I assume that if they declare independence, their currency should be 1 : 1 RM. If Johor capable and able to develop well, my guess of exchange rate will be SGD 1 : 3 : RM 6. I think it will be time for Johorian enjoy 1 : 2 exchange rate.