After lengthly discussions and reviewing the different opinions and options for skins I would like to move 2.6.0 into a release using a skin similar to Synthetica Blue Moon (we can not continue to use it due to license issues). The best choice in the moment is JTatoo Luna which will keep a 2.5.8 like appearance and will not cause discussions within an existing user base in a setup that has a large userbase (e.g. a company).
IMHO the Spark client should focus on larger deployments inside organisations/companies. Those groups tend to have a conservative look and feel and they have the need of keeping the user experience the same after an upgrade.
While I understand the need for a "personal" touch by using a skin, I would argue that this is a need of a minority of the users.