I see no reason why there can not be more than one running at the same time. As we had last year, by the way.
We have a lot of members, and a lot of subjects. We have members that only do armour, others that only do aircraft. I doubt that there will be serious conflicting interests.
Also as you point out, there is six months, so All will have loads of time to join in if they wish.
The only change in the SIG "rules" are that anyone can suggest an SIG at any time, there just has to be a minimum of ten participants or it will not get a forum set up for it. The subject has to be more specific.
Ian M