We tried this already with SWAT and SRT, they forced you to be a SSGT+ in swat to even join SRT and it was a huge mess because people were kicked out for "not being the proper rank required to join the department". No-one liked it and the department became inactive. So, no this would be a horrible thing and on top of that who's to say that people want to merge the Tac teams. You're gonna be forcing people to re-work their training and ranks into merging tac teams which would basically be trying to fix something that isn't broke. I don't see any up side to this, with forcing this down peoples throats. in turn the major problems with this is we have different ranks (SRT has the USMC Ranks), every tac has their own unique thing and training, and you're forcing people in departments they don't necessarily want to be in. Another thing is you realize that everyone has different training right, we also have different specialties such as the obvious SRT has Parkour SWEP, or how about the command structures how is that gonna work you have an OK idea but there are just to many factors to be put into play such as oh shoot we have 5 commands and Co-commanders what are we gonna do divide 5 Tac Teams into groups of 2? How are the ranking systems gonna work? How long will the roster be? how hard will it be to get into the new Tac team once its created? How long will it take to merge the SOP'? There are so many unanswered questions to be solved. Also, you say everyone would be able to keep their rank, that's incorrect I can't find 1 Tac unit besides SRT that uses USMC Ranks so if you would like to tell me what Gunnery Sargent and Master-Gunnery Sargent would transfer to please enlighten me until then lets leave the Tac units be. If people want to join a different Tac team let them do it themselves don't force them to do it.
Overall, you have an OK Idea that would work on paper but once put into reality and into the server its gonna be a shit show. so you're getting a -Support from me