Thanks for the quick answer.
I would be happy to chip in say 25% of the buy price a year for updates, for me a far better option than having 10 versions of the same software. Its less then buying a new version SW after 2 yrs. I'm a developer my self, so i know it's lot of work, time (so money) to push updates. I hope you will get more popular and maybe as new children are born every day, so every day someone new needs a design tool, maybe it will be enough to keep Affinity up to date.
Hopefully apple will also make some effort towards paid upgrades. I guess, we will have to see. At least i hope you will stay by you answer and push updates for the next 18 months.
I still have to evaluate (as I already have a similar tool - if i would not, i would buy Affinity right away) but your answer did push mi more towards the buy side.
Thanks