Perhaps it would make more sense to ask the community first since that's what OpenWrt struggles
I've decided to kill two birds with one stone instead (cheated, took a shortcut, name it as you wish). I've instead decided to ask developer community, team members, fellow developers, people already using the current tools and let them make the binding decision by actually voting for their favorite. So we get survey and the usable results, which would translate into actual action in one go.
I did so, because I think, that if this established voting mechanism is good enough for other topics, it should be good enough for this decision as well.
On the other hand, I've decided to ask wider community about the new project logo/colors, because they're actual users of this change, they're going to look at it for the next few years 
The result and feedback was amazing, so I plan to use this kind of decision help in such suitable topics in the future as well.
BTW evaluation of GitLab as next platform has started around 7/2019, right after the Hamburg 2019 developer meeting, IIRC you were aware about that intention since it was discussed in public since then and you've even suggested to do such survey, but actually done nothing in this regard by yourself. Don't blame me now.
Anyway I really think platform like github or gitlab should NOT be dropped
There is no such option in the voting email, or is there? The question is: What should be our next development platform? I don't see anything about closing GitHub. GitLab.com/openwrt is for evaluation only since the beginning and could be disabled, that's correct. FlySpray is probably going to be exchanged with the issue/ticket feature in the selected platform. Patchwork OR similar mail based alternative is going to remain, this is 99.999999% sure
It's really about having somehow blessed path/direction, because other planned changes (issue and review bots for example) would mean tighter integration with the selected platform and nobody wants to invest time in the almost "phased out" platform, thus throwing some non-trivial work away.