I invested in a m43 system, whilst it was easy to use, good IQ and light weight, something to consider is the cost of lenses plus ports. Each lens required a port specifically for that lens and the costs/investment I found was very expensive. If money is not an issue, then it's a great choice, however for me I need to sweat the asset and had to re-consider my options.
I use my SLR on land, with a decent lens collection already, I have now housed that and I have found it a much cheaper option and it has dual use for me. The m43 camera was v nice, but It still couldn't compete in many ways that were important to me than my d90.
M43 is a great choice, but i've read people say total cost of ownership will be a lot cheaper than SLR, I think this is far from the truth in my experience and i'd look at the type of lenses you 'might' like in the future. The 'used' market is quite small also, so buying new all the time is also quite costly. I'd way it all up before diving in.