Doing something like "pkg version -vL'=' can take several minutes especially on smaller devices. During the whole time the database is locked. This prevents any port being installed or removed. 
What I think is happening is something like this:
pkg creates a read cursor on the database and then walks from entry to entry to obtain the ports version through some make command.
What it could be doing instead (to prevent the long locks) is something like this:
Take the output of the query that was use to create the cursor and put it in a list then process that list as it did with results of the cursor.