Will installing this mod have implications on upgrading to phpBB3 do you think? If so, what is it likely to mean?
I have never tested an upgrade from phpBB2 to phpBB3 with or without Approval MOD installed so this is purely a speculation, however, it would be quite logical to assume that phpBB3 does not require any files
from phpBB2 installaton (with the exception of the config.php file, which is not touched by any MOD anyway).
What phpBB3 will use, naturally, is SQL data in the phpBB database. Since phpBB3 is totally unaware of the SQL fields added by the Approval MOD, I expect the upgrade procedure to discard the Approval related information and simply take over the posts as if no Approval MOD was installed.
What is essentially means is that if my thinking is correct
all your unapproved posts will become approved after the upgrade and users permissions such as 'Allowed to approve' / 'Always requires approval' / 'Never requires approval' will simply disappear together with the Approval MOD itself. The moderator status should not change.