yes, but even so, his showthread template could have a condicional
Code:
<if condition="in_array($forumid, array(1,2,3))">
showthread2 template
<else />
normal showthread template
</if>
of course, I know what you mean, the showthread.php will be the same, but manipulating the template should allow to change pretty much everything about the way the data is displayed.
You see that in the first post his concern is how to display the showthread 2 template, he doesn't want to change the core.