From available info (translated and otherwise), my guess is the TOH will be:

1. at launch will be nothing more than fancy rainbow coloured covers.
2. able to be expanded in many ways later on (depending on 3rd parties as well as "maybe" Jolla themselves)
3. confusing everybody and causing Internet arguments until launch date

Now, my thoughts above IMO are the most logical, cost effective, and probable from the info that we've seen so far. Unfortunately, the bit about 3rd party TOH is a worry for me; it's highly unlikely that any 3rd party will produce anything with a reasonable economy of scale because... well... I don't think Jolla is going to be shipping 50M Jolla devices per year. So, if there are 3rd party TOH, they'll most probably be at a premium (or be less widely available than Jolla was when pre-order opened). Which leaves TOH from Jolla themselves... but I just woke up and my brain stopped working at this point, so I have no thoughts on that.