Eve was horrible for a long time after release, but it was the only working sandbox at the time. You can't compare their subscription sequence to that of Perpetuum. And the influx of Eve players to Perpetuum should have no bearing in any argument about subscription numbers and their relation to game content.
From experience, I can tell you what a huge deal Eve made out of their exploration implementation. Eon Magazine had an entire issue with pages and pages of pictures and stories and faqs about the new system. It took years for Eve to put that into the game, and it took months to iron it out and balance it. Perpetuum added it as a small update.
Every nugget of content the game adds is a good thing in many ways: it adds content for all players, it draws in new players, and new players add new opportunities for all players. Beacons are awesome and seemingly simple. If they can continue to add content like this, it is a win/win for everyone.
The games progression should not be judged by a contrast to another game and certainly not by a sub ratio. The game's progression should be judged by just that -- the games progression. Content added can be judged independently of the game itself; however, in this case, I think the judgment’s outcome will be great.