You obviously don't know much about kicking in stand up. Let me educate you. You can't block kicks like you can punches, if you do you are going to get really battered arms that you won't be able to punch with after a while and could even get them broken. So to block kicks safely and effectively Floyd would need to learn a new way of blocking. It's not easy to relearn something you've been doing another way all your life. And that's just body kicks.
If you try to defend head kicks the way that Floyd normally defends head shots then he's going to get knocked out. The earmuff defence won't work very well against head kicks and he's likely to knocked out if he does that. The sway back shell defence that he often uses won't be effective against kicks either because unlike punches a head kick that glances off the top of your head is still very likely to KO you. And he'll have to learn how to defend the knees as well. Tenshin has brutal knees that he like to finish his combos with.
And that's not even covering low kicks which would be totally new to Floyd. Floyd's legs would give out after just a few heavy low kicks. And he won't be able to learn how to check without a lot of investment which at his age is very unlikely.
Floyds defence is great, for boxing but he doesn't know kickboxing and he'll have to learn a very different way of defending. I don't think that's likely given he's 40+ and has been doing one sport all his life. What's far more likely is Mayweather chooses the rules and doesn't allow Tenshin to do anything other than maybe kick above the waist.