Apart from the perimeter limit, LGA's runways are also only ~7000ft.

I don't know what Boom's expected runway requirements are, but if they're anything like the Concorde's (>11000ft), there's no way they'll actually be able to take off from LGA.

Edit: At least one source says that Boom's plane requires no less than 10000ft[1].

[1]: https://www.aviationtoday.com/2018/11/13/aerion-boom-taking-...

The LGA perimeter rule already has holes. Denver is allowed, and the rule doesn't apply on Saturdays. With the much more airline-friendly layout post-construction, it would not be surprising if the rule is changed.