Hi Philipp,
Thank you for your support! 🙂
Developer Licenses
Currently, no “developer” subscriptions are available nor planned as of yet. What is however planned are “multisite” subscriptions.
The latter will take quite a lot of time to implement and develop (maybe even half a year), as such implementation takes in many factors (allowed extensions, network-active extensions, network API, etc.). These topics cover both free and premium extensions.
If you own a MultiSite network, feel free to send me a private message on my contact page (links further in this reply).
One per site
Each site will require its own subscription. However, I do not believe each and every site can benefit from such subscription; as the (planned) “premium” extensions are quite use-case specific. Time will tell if this holds true 🙂
Still under maintenance
The shop is still under maintenance, because (unfortunately) I was ill in the holidays; so that part didn’t make its deadline of 1/1/17. When no more “opening soon” message is displayed at the top of our shop, then it’s open.
Upcoming Extensions
On The SEO Framework’s GitHub issues page, labels are placed for whether a feature request will become an extension:
1. Free Extensions.
2. Premium Extensions.
With that, the answer to “planning for an advanced sitemap”, is yes 🙂
Alas, no ETA for those is in place yet.
These forums are for free plugin support
If you have any other billing or premium-related questions (I should make a sticky about this; Edit: Found here.), please forward them to our contact pages: Before Purchase, After Purchase; as I don’t believe I may answer them here.
So, with free plugin support, these topics are covered: plugin/extension activation, free extension and main plugin bug reports, (free) usability questions.
Any questions about premium extensions, billing, licenses and even security should be inquired through the links above.
Thank you so much! Have a wonderful day 🙂