Ok first,
couple questions
Do you even want more range? seems as if you don't, or you might have mentioned it, If you do then maybe do sell it or trade someone with a S/SR/DS who wants a smaller bike, add a little cash... just a thought then you don't have to hassle selling and buying new again... maybe you do want more range and that is a good option like terry said
Second
Have you ever overheated your FX? Have you ridden it flat out for 2min-10 min WOT? Do you intend to be going Freeway speeds at over 80MPH? or do you ride streets at 60? or less?
Third
You mention ABS do you want abs? I honestly wouldn't even bother, but I'd probably be considered "risky" on here anyway (Im 25).
And where are you located? where are you moving to? Do you have a dealer in your area?
without your answer on those this would be my take...
Way to much effort to get zero to sell your dealer the IPM motor and do the conversion.
Now you can put S wheels on it and have a Supermoto "FXS" without the IPM motor
the IPM is much less likely to overheat, but if you havn't overheated your fx, i wouldn't worry about it.
NOW that being said, when you go to S wheels you will loose a little top speed if you arn't traveling 80 mph trying to keep up with huge city freeways, I wouldn't worry about it.
Harlen can probably get you everything you would need.
If he would let you, I would buy ONE DS fork the caliper side one, that way you can have the travel but S wheels, and the caliper will bolt right up.
There is also an adapter he sells to hold the MY14 S/DS caliper in the right spot for the bigger rotor on the S front wheel, rear should be the same, within MY14. I haven't asked him or done this, as I always changed the forks to S forks, DS forks, I've tried it all once or twice... eventually ill get some time on some showa zeros