I think having a couple courses done with the Winter theme (as there are now) is nice as a novelty.
But I wouldn't want to see 1000s of them, as the novelty wears off.
Plus, if including it would take any resources away from anything else, then no.
If it were totally "free" from HB's perspective in terms of labour/allocation of resources, then sure, as there is no downside.
Though, as an aside, it would be nice on the course select screen, to have the theme indicated by the course name.
Some themes I enjoy more than others, ps4 runs better than others, etc, and sometimes you want to play a particular type of course.
Having that on the front page would make those selections easier (and if people wanted to avoid winter themed courses without winter in the name, they could do it quickly/easily)