Bristol and Gloucester want him back, but so far the rumour seems to be more fear that he's out of contract and we haven't heard anything / wishful thinking from Glos.
Far more likely that Charteris is to replace Hooper, who's expected to retire at the end of this season.
Bath also rumoured to have been looking at Ritchie Gray (likely lost out to Charteris, who we've hunted for years).
Bath have both Attwood and Hooper out of contract this summer; with the latter likely to retire.
We then look at a couple of line-out specialist locks. To me, that suggests that we're looking to replace out line-out specialist, not our enforcer; but hey, logic doesn't always apply to these situations.
The only way I can really see validity in replacing Attwood is if we over-paid to get him in the first place and don't want to increase his pay.