The major legal obstacle is that many ultralights don't meet the requirements for an E-AB aircraft. First, someone has to have built it for educational or recreational purposes. The thing must be instrumented in accordance with 91.205, etc. (yes I know that says for standard airworthiness but you can bet you'd have difficulty if you don't meet at least the day vfr requirements). Your plans-built planes are one thing, someone's fat QuickSilver two seater is another.

The issue is taking some factory-built aircraft that doesn't meet the 103 limits and doing something with it, NOW. The grace period for moving these things to LSA is past and there's no legal way forward.