Liiga is going to be (and actually already is) closed series. Mestis is more like AHL is to NHL.
The change isn't as dramatic as it sounds, because teams very rarely raised from/were relegated to Mestis. Most mestis teams aren't economically close to Liiga teams, so the relegation was seen pointless.
Champion of Mestis can apply for Liiga licence in the future, too. It has to meet the economical and arena standards and be able to pay the Liiga licence in order to have a chance to be accepted as expansion team. Sport and KooKoo have met these standards.
Source:
http://yle.fi/urheilu/liigakarsinnat_lopetetaan_-_mestis-mestari_anoo_jatkossa_nousua/6994431
If Liiga actually becomes 16 team series, the playoff spot will be worth more than before, which is right direction. Just getting into playoffs could make little hockey boom in the town.