Developing the regulations for OFB and FB tournaments.

Could you organize a tournament among the top 8 (10, 20, ...) players based on their ranking from those who didn't qualify? There was a desire to make it more valuable.

I didn't quite understand. If you mean expanding the number of participants in the wildcard tournament, then this is quite reasonable; let's say up to 16 participants. In this case, the motivation to fight for a higher position in the OFB will also increase.

The main problem with the OFB is the Swiss system, in which players who have lost their chances of qualifying for the FB continue to participate.

I don't consider this a problem, as objectively, more than 50% of the participants don't have a chance of being in the top 5 even before the tournament starts.
I judge by myself; when I register, I perfectly understand my strengths, and the OFB is a tournament for me and most players to gain experience and practice playing against stronger opponents.
Therefore, the lack of motivation is an excuse for unscrupulous players, and a system that reduces the number of such players or at least reduces the likelihood of such behavior would be quite useful.

In my opinion, a round-robin format is not the best solution for the FB. In addition to the motivation issue, there are no decisive games or a final that would attract a large audience. The top 2 players could play against each other in the 4th round and then just start eliminating each other.

It is possible to develop a draw system in which 10 players are divided into 2 groups based on points, and the top group is matched with the bottom group to postpone the meetings between the leaders to the final stage of the round-robin tournament.

Or, as an option, a final four after the round-robin tournament: 1-4 and 2-3, and then the final (but this will require approximately 2 additional months)