WWE has 51 women wrestlers (or is it 50? I don't know if Scarlett wrestles but I counted her) across all 4 brands. If you consider the 4 singles titles and their respective challengers, injured superstars and Charlotte Flairs chops off half of those, that's 25 performers, so I fail to see why they can't have an active Tag scene. Have the champs do a feud on one RAW, then SD, then NXT, and then NXTUK. While the champs aren't on that show the teams vie for the #1 contendership for the brand. Simple as that.
Say Shotzi Blackheart and Tegan Nox win the Championship on Wednesday, they then go into a feud with a RAW team for a month, then after defending the belt there move onto Smackdown for a couple weeks, then make an appearance at NXTUK (maybe have the UK people come Stateside if need be), before feuding with an NXT team.
The Womens Tag Team Championships were supposed to be a travelling championship so if they just did that regularly it would be perfectly viable, and give the Womens undercard something to do instead of fighting over hair color or choice of romantic partner.