It's already like that. Older nodes gets more coins from validation. Also gets coins from making flips (0 epoch node don't do flips for first validation and can do less flips for first few epochs), do not have an option to invite someone and get invitation rewards before epoch 5?. so person who is killing his node each epoch is mining like 2 times less than 5 epoch old account thanks to validation rewards. 5 epoch old account is a 100 day hodler... that super long comparing to average in crypto.
About coins outside of stake - you cant block people from spending their coins its not what its all about ... all you will get is making new nodes enter the network harder = slower network grow = lower fundamentals. You need to build use-cases that will burn coins (like ADS network that should be done in this year) and other activities. You need to make access to idena as easy as possible. Otherwise you will make all this dumpers to join farms, because farms will pay them after each epoch from coins dumped from older nodes while holding "dumper" node coins till "full node maturation day" to dump without penalty.
Its not tokenomics what makes idena to be locked in super low cap coins range. Its lack of marketing and big exchange. Not surprising. Before validation sharding price explosion is dangerous.