I'm torn with this same delimia. I'm on 4.1.0, mostly because I haven't used my Switch since the BotW DLC came out, but now I kind of want to play MK8 and Splatoon 2 online. I haven't even been bothered to boot into RCM (I did try for about 30 minutes but gave up), mostly becauae I don't need anything it offers at the moment. But that isn't to say it won't ever, and that's where I'm torn. I don't need to play online right now, but not being able to makes me want to.
I'm rambling because this post is as pointless as this thread, because it's all based on maybes and speculation of stuff that could happen later. And for all we all know, 5.1.0+ could get the same goodies down the road. Early scenes always say never, but if I've learned anything from the PSP, Wii, PS3, 3DS (especially the 3DS), Vita, PS4, etc scenes it's that everyone in the beginning love to say stuff will never happen. They buy expensive flash cards, weird tools, and dongles while changing headers and getting banned, soon followed by an SD or web page solution brought to you by some awesome dude/lady that does everything you thought would never be possible.
Or something like that. I think I'm going to go update and play my games I paid money for online and wait until something cokes out 2 years from now that will let me play all those shitty games for free that I couldn't justify spending money on.
TL;DR update, or don't. You never know what will be released tomorrow.