Spent some time today doing more research on the fuel injection kit for the Rotax.  Looks like there are several options I could pursue. See here for the source of the various kits mentioned below.  See here for pricing on the various versions of Rotax engines.

From easiest conservative path to more radical and time consuming:

1. Use stock Rotax 914 as is.
2. Using 914, replace the Bing carbs and ECU (Engine Control Unit) with EdgePerformance's EFI kit (4-1 Intake version).  This option would have a modest performance increase, but perhaps ~20% fuel consumption improvement.  I don't know much about the ECU, so it may or may not be as redundant and robust as the Rotax system.
3. Use 912 (80hp version), turbocharge (or supercharge) it and add EFI kit.  This should be the equivalent of #2 above but perhaps much cheaper (though more work).  See here for more info on this and #4 below.
4. Use 912 (100hp version), turbocharge (or supercharge) it and add EFI kit.  Not sure of the resultant HP here.
5. Use 912 (100hp version?), turbocharge (or supercharge), add EFI kit and change cylinders to bigger bore (various sizes available).  Most power, most work.  See here for more info on the various big bore kits.

Note that except for #1 the Rotax warranty will be voided...  Something to seriously consider.   Well, I have close to a year before I have to decide about this.