I think that there needs to be a meeting of promoters of both current league in June / July next year to discuss 2027. There's no point leaving it until after the season ends. If there are disagreements (which there obviously will be), there needs to be sufficient time to arrange follow up discussions and come to some compromise.
If there could be a big 'reveal' meeting (and try to get as much media involved as possible), it would be a good start to the new era. Maybe a change of name for the league as well - the British Speedway Super League perhaps?
''Dormant' and potential new tracks can get involved, riders could make plans, supporters could consider season tickets as Christmas presents, media can get engaged.