AHHHHH. Whenever anything is successful it goes centralized, is this also happening with MASS? Reward going down for people that have low storage means people with high storage volume will get bigger piece of cake. This is exactly whats going on in BTC.
This is true for any coin that can be mined. All coins are subject to increasing mining difficulty over time. However, unlike CPU/GPU mining, mining on HDD is more resource-intensive. It is more profitable to buy videocards than capacitive HDD/SDD (4-8TB or more). And no one can prohibit single miners from joining pools; this is historically the case.