I would absolutely buy all seven seasons of DS9 on Blu-ray, on release day. I generally wait for a good price on TV seasons rather than buy them straight away. But with DS9, considering the work CBS is putting into remastering Trek and the astounding results, I wouldn't want to wait.
But as for the wisdom of releasing DS9 on Blu-ray, I hope CBS realise that they have an opportunity to market DS9 in a different way to the other Trek shows. Because it's more serialised and the characters' actions are often morally ambiguous, it has as much in common with contemporary serialised dramas as it does with traditional, stand-alone Trek like TNG and Voyager, certainly in the later seasons.
Consequently, I expect a number of new Trek fans will be surprised to discover what DS9 truly is. Anecdotal evidence seems to suggest that DS9 is being discovered on Netflix and other sources and re-evaluated, free of the competitive assessments during its first run. If CBS choose to market DS9 as an epic, sophisticated drama series as well as another Trek show in HD, they may reach fans on the fence or just people curious about good drama. Promote the fact that DS9 anticipated shows like Battlestar Galactica. Use DS9's critical acclaim to your advantage. Don't just put together a trailer with cliched Trek dialogue, phaser blasts, and aliens doing funky alien stuff. Think bigger. Sell the narrative and the world.
Honestly, I've been disappointed with how little attempt is ever made to distinguish the Star Trek shows in marketing terms. Here in Australia (as in the UK), the slimline DVD sets for all four modern Trek shows follow the same visual template: ship/station, with the captain and another cast member behind them. And on the back, there is NO TEXT at all. For a Trek novice or a casual fan, they have no way to tell how the shows differ from each other and determine which one is for them. No-one would even know ENT is a prequel. The assumption on CBS/Paramount's part seems to have been: the fans know what they want, and no-one else cares, so we won't even bother writing any copy describing the season, or slap a couple of enticing images on the back.
Of course, I'm aware that Trek home video sales have likely been driven largely by Trek fans, and that CBS/Paramount might well have known exactly what they were doing in keeping the marketing minimal. Perhaps the public stigma of Trek is so powerful that it's actually more useful to play on it to welcome in fans than try to overcome it to attract new ones.
But if there is such a concern - and understandably so - about DS9's commercial viability in HD, then I encourage CBS to step outside the traditional Trek marketing box and use the show's progressive approach to their advantage. Arrange media coverage discussing the distinctive aspects of the show. Put together trailers and posters that even make Trek fans agog at how cool DS9 seems. The TNG season 2 trailer on the first Blu-ray demonstrates that CBS can craft a grand, enticing piece of marketing, even from a 1988 season of stand-alone episodes. I hope they take those skills and make DS9's differences from the other Trek shows a marketing asset rather than something to be ignored.