JM just posted a concept pic in his blog of the new updated RG design:
Rail Gun Pic
When first looking at it, I though that was a new form of energy weapon that they'd be introducing in S4. Although after reading further on down the page it was revealed to be a Rail Gun.
The only real good thing about seeing that instead of an energy weapon would be that it looks to be portable, although that may be the way they're put on the 304's, but it reallyu does look like it's mounted on a portable platform than anything else. So maybe they are installing them on Atlantis, for events like 'The Siege II'.
Spoilers for 'The Seer':
The second thing, is to see if they've been improved via use of the Asgard knowledgebase. So maybe they're able to shoot into orbit this time & reach Wraith ships!