Would be nice if I could also upgrade ghost belts. I'm assuming this is planned due to this error message?
'Belts of type "entity-ghost" are not yet supported for tier-based upgrades. Please contact the Belt Thread Upgrades mod author.'
It is on the todo list, yeah (you can find the current todo list on the github repo). It is just tricky since the method I currently use to build my network relies on links available from the built belts, which ghosts aren't as obviously suited for. But it should still be possible in some form.
