Faust it would be a good idea to lower the price, but they would need to analyze whether it would increase sales a lot to compensate and we also don't know if it has been selling a lot or a little at the current price.
Gitlab was certainly just an example, but I believe that the future is Open Source + Cloud.
Unlike Xenforo, which already has a Cloud solution as well, so if the base was Open Source, they could still earn revenue with the Cloud, which has another target audience that wants something managed and ready.
I also agree with the risk of having resources stuck only in the Cloud, but as Xenforo already has the Extensions I think it would already avoid this, Gitlab itself suffers from certain resources that it only has in the paid and more expensive plans
, it depends a lot on who takes care of it of business.
And for those who host on their own, they would gain with the increase in the community, more professionals to maintain the tool and the extensions such as the gallery, advanced search, resource, branding and others would keep paying, soon they would increase their sale as well since the amount would increase of Xenforo users.
Open Source project by itself is not usually profitable, but what it does around it yes, like Plugins market, Cloud, Consulting and etc, Opencart worked this way for more than 13 years and certainly earns very well, same Wordpress is worth it, now imagine the best Forum system doing this, there would be no competitor to hold
Now of course they are ideas, there's no way to know what would happen, but at the very least it would greatly increase usage and users and with that the chance to win with extensions, consulting and the Cloud.
What Xenforo needs maybe is a bigger team and more community participation, but neither, because I don't know the size of the team and if they work full time in the tool.
Summarizing my view:
More Users > More Cloud Usage and Extensions -> Funding for the project and capital for the company and the team