that's a possibility but until northern hemisphere coaching and style of rugby catches up to the all-blacks/new zealand franchises in super rugby i think there will always be a pull to staying in new zealand
as a wasps fan i have to say that im absolutely elated that sopoaga's coming, even if it does mean the end of danny cipriani's time at the club
sopoaga and jimmy gopperth could be a lethal 10-12 pairing especially with elliot daly outside them (when he's back from injury)
i do understand why international teams in lots of cases only pick from players playing at home but it does often make me wonder what could have been both at club and international level - i would have loved to see stefon armitage and nick abendanon play for england again and id have loved to have curtley beale come and stay in the northern hemisphere too
what's crazy though is there is a championship (2nd division) team called bristol that has just signed charles piutau to the largest contract in the world - the fact that he and his brother are gonna be playing together again in the premiership next year for a newly promoted side is both ridiculous and tantalising but it's a shame that charles piutau wont be available for the all blacks because he's a stunning player at full back/outside centre
SANZAAR is kind of a basket-case of unique problems, from South Africa having the internal politicking but the most financial clout, Australia being more stable but having to compete with about three other major sports (sidebar: they should have merged the Rebels and Brumbies and kept the Force, but I digress) and NZ having stability and a ton of talent but an absolutely miniscule market (with a total population of 5 million or so we're lucky to compete with some European cities, much less entire leagues and broadcast deals). But the day the unions let overseas players compete internationally is the day Super Rugby pretty much dies completely and the rugby scene emulates football with all the money and talent being in the clubs - which leaves everyone over here high and dry.
I get the development angle (and the domestic cup here, despite being a financial wasteland, is probably the best development league in the world for both players and coaches) but I think that leaves Super Rugby facing a best-case scenario of becoming like what the NCAA is for the NFL and NBA but without the glamour. A situation where players slug it out for a few years in the south to learn the craft and get drafted by European clubs could be kinda cool if everyone got into it but I think the north would be getting the better end of that deal. Sadly I can't envision anyone in Europe getting up at 2am to watch potential draft prospects and I can't see people here giving a fig about players that everyone knows will head overseas for their best years.
With that said, you're getting a good player in Sopoaga and with the (admittedly little) I've seen of European rugby a lot of southern hemisphere stars seem to do quite well over there. I remember going to the Saracens-Tigers semi-final a couple of years ago and it was kinda cool to see Michael Fitzgerald being a fairly big part of Leicester's pack - he was one of the veteran guys who always stuck around for the union where I'm from (which is one of the smallest in the professional game here but still). And I remember being amazed by how long guys like Rupeni and Doug Howlett were able to keep playing at a high level for their clubs. Forget Kurtley Beale, you want to imagine how guys like Israel Folau or the Savea brothers make their side look.
In the future I think Asia could be the interesting x-factor in how the game ends up looking, with rugby on the rise in a lot of places and some broadcast deals on the brink of expiring. What I'd be interested in is the viability of cutting South Africa and Argentina loose domestically (albeit sticking with the Rugby Championship) and focusing on consolidating with Australia and Japan. The ARU did some extensive auditing a few years ago and that seemed to be the model recommended to them. Then see what kind of Champions League-esque format can be worked out in the global calendar. See if you can't end up with a truly global game from both a club and international perspective.