there's also Colonia, about 60 systems on the route between Colonia and Sol many in interesting places, Explorers' Anchorage near Sag A*, and a substantial number of settlements in various nebula out to about 7000 LY from the bubble, which could all be their own starting points.
As
@Alien commented, it was clear that the intent for the beta is that only systems in the bubble are to have a colonisation contact.
But it does seem that allowing colonisation to start from the out-of-bubble places you mention, especially along with a moderately expanded claim range, would be the best option for satisfying the less bubble-oriented playerbase while not introducing arbitrary new mechanics like some of the suggestions here (range for arx, range for credits, range for star density, etc.) which are probably non-starters at this late stage in development.
Assuming there's no dependency on nearby system resources or trade opportunities for colony viability, that is. Though sourcing colonisation goods at remote locations may well provide challenges already, possibly requiring multiple carrier loads to be shipped from the bubble, depending on numbers required.
To shake out "interesting" situations (like the detention one) that will crop up with out-of-bubble colonies, and maybe gauge the interest in it, it could be worth introducing remote colonisation contacts at some point in the beta.
Regards the detention issue specifically, would this already be a possible outcome of odyssey crimes at systems like
GM Cephei with its numerous settlements?
Maybe we'll have the option of adding a local penal station / settlement to avoid this!