The Splinterlands game itself is not getting abandoned by no means...
As the team stated, there are separate teams working on all these projects at the same time. The Splinterlands team itself is the largest still and they are the ones churning out all the development for the roadmap items.
In terms of card holder benefits, owning cards is still very, very valuable as SPS rewards will begin soon for those that actually play Splinterlands. So through Brawls and Ranked play, you will begin receiving SPS. With this SPS, you will then earn other rewards if you stake it like with the GLS airdrop...
To sum it up, if you are a Splinterlands player, this extra project is only going to reward you even more. It will bring new people into the ecosystem and will only help the game grow!