Is it possible to use Stripe ability do pay in several times for a subscription ?
I mean if we have a plan priced 1200 €, can Stripe SEPA offer a 12 months payments for a one year subscription ?

Create a by calendar month duration plan with a price of 100 € and that's basically what you'll have. There is no duration usage in CBSubs to subscribe for a year, but pay monthly. This doesn't really have anything to do with SEPA or Stripe though and is a feature that just doesn't exist in CBSubs.

I have read that Stripe allows to have one subscription divided in several payments with its model. Could you implement it ?

The thing with monthly subscriptions is that we need to have a compulsory 12 following months for our business model. So is it possible with CBSubs to make 12 consecutive compulsory monthly period ?

No, something like that needs to be implemented in CBSubs it self to subscribe for 1 year, but bill monthly. If implemented in CBSubs I'd then update the SEPA implementation to create a mandate for the yearly amount, which would just be charged monthly but again there is no handling for this scenario in CBSubs.

Regardless at this time the SEPA implementation is disabled. This is because Stripe has a bug with their SEPA test credentials and I am unable to test the implementation of SEPA payments (all other methods are tested working). I've already contacted their support regarding this, but I won't be enabling SEPA until I can confirm it actually works.

I think the closest you can get to what you're wanting is monthly duration with "Total number of occurrences of regular validity/price (0=unlimitted)" set to 12. This would bill them 12 months then expire the subscription.

So is this on your roadmap ? is this hard to implement ?

Additional plan duration types are planned, yes. As for when I've no idea.