It saddens me to see the population on worlds so low nowadays, however with that being said. I really think everyone is underestimating the lifespan of Runescape.
Nowadays it seems like 10% of the players left from the 'glory days' make up 90% of the Runescape profit. Micro payments, 07, etc.
I could see Runescape being around for another 5 years or so. The numbers will never be as high as they once were, but it'll stay around. There's always going to be people playing. Now at what point does it get to where Jagex says we can't operate anymore- idk.
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Here's my theory on why Runescape won't grow any larger than what it is currently at.
I personally started playing Runescape in 2005, and I'd be willing to bet that the majority of you started plying around this time period +/- a few years, right?
Well, look at the game as what it was then- Simple as could be. There wasn't a flashy tutorial island trying to impress you, items worth billions of GP, or a stuck up "veteran" community running around complaining about how bad the game is and how it was better in the "golden days".
For me, Runescape was simple enough for me to really get into and want to "explore the massive MMORPG by Jagex Ltd." Yet, extensive enough to where I was always challenged and kept me interested with the game.
If a new player was to start playing Runescape for the first time ever today what do you think they're impression would be? Terrible. Hell, it's even terrible for me since I don't play EoC much.
Jagex has been catering (Trying, but failing to do so) to the current player and sucking every penny possible out of them. They said hell to the new players we're not getting many of them nowadays. Which if they attempted to, the health of the game would look much more promising now.
Anyways, I'm going on a little temper tantrum here so I'll stop typing because I know you've stopped reading quite awhile ago.
TL;DR No new players; Game dies eventually.