It's limiting on purpose, this forum is specifically for people who collect SteelBooks.
"SteelBook" is a brand name, and there is an entire sub-set of collectors who collect only SteelBook releases. They tend to be very limited in production and often retailer exclusive which means they hold their value much much better than other types of packaging.
This site started out with a very narrow scope but what we do is that when a new area of collecting gains enough support and enough knowledge we expand to cover that area as well. SteelBook collecting is one such area, which is why a SteelBook specific forum was created.
We have
a general "collecting" forum for discussing other types of movie packaging and other types of collectables.
Even if movie collecting were to become popular enough to have it's own forum I would think it would still be separate from the SteelBook forum.