Smaller, faster? Faster: no such thing. Eh ... AW139? Well, fine until the day you are 150nm offshore with IMC at your destination and no space to do proper work on your casualty.
The 139 is easily big enough to cope with that regardless but that would be a job in the very small percentage that occur more than 100Nm from base according to MCA stats so what is your point?
As I have suggested, a couple of longer range bases with big helicopters for those rare jobs and smaller, more user-friendly (from a winchman and casualty perspective) for everything else.
We don't have to go down the mountain HEMS route - I still think winching is far better than long-lining - and you need to be able to move MRT around but a 139 sized helicopter with lower downwash has to be a better option for coastal and mountain work.
I know a manufacturer won't design a whole new helicopter for SAR but offering an option with a longer tail boom to accommodate a larger rotor and thus reduce the downwash wouldn't be that difficult, would it?