At work I keep on finding people writing things like 'tonnes of experience'. At first I corrected it; it was obvious to me that the old words should be used in old expressions. But as it kept coming up, I googled it and found there's now plenty of it out there. People have apparently adjusted to tons now being called tonnes and are using the current spelling even in the figurative way. I suppose they pronounce them the same, so it makes no difference to them.