Hey john,
For me It was easier to think of the new system in the old way terms, so I think I have a good handle on how it works.
for simplicity i will use 200 dollars as the "upgrade" price even though there are other avenues for a cheaper price.
so in old way thinking,, it is 200 bucks to "upgrade" and i want to "upgrade". cakewalk has been so kind to offer me two ways to pay for my upgrade, you can pay the whole 200 bucks or if money is tight they now offer me a payment plan to pay this "upgrade" price on a monthly installment plan for a year. the installment plan will contain a small processing fee so I will pay a little more than 200 bucks for the "upgrade" on the payment plan. if i choose the monthly plan I have not paid for my "upgrade" unless I pay the 12 installments. Cakewalk has advised that every year you will have the same choice to purchase the "upgrade" upfront or in a monthly plan.
to your original question? whenever you decide to buy an "upgrade" you are at the most up to date version, immediate catch up. If you decided to pay up front you will have the most up to date version up to the next "upgrade" version, old way thinking of yearly upgrades which would be a year after you jumped in. If you choose the monthly payment plan, and you did not pay for the whole year 12 payments you would drop back to where you were when you jumped in, assuming that would be X3e. if you did pay the whole year then you would stay at where you are as if you paid the 200 upfront. if you decided not to "upgrade" the next year that is where you stay. so if you jumped in today and paid the 200 upgrade fee or paid 12 months of the installment plan and did not want to "upgrade" next year you would stay at the version as of 2/24/216
most simple way of thinking if you have paid or are paying monthly you have everything you could possibly have for whatever version you have artist, platinum, etc.,, if you have not paid or stopped paying monthly you will have the version that you last paid for an "upgrade". for this year it would be x3, x2, x1 whatever version you were when you jumped in.
Next year you will stay with the version you paid for a year so if you jumped in today and either paid for a year or the 12 month installment plan and did not want to continue "upgrading" you would stay with the version of sonar up to 2/24/2016.
Mixing the old and new way of thinking cakewalk has decided not to hold their improvements to just a once a year release they will release the improvement or new feature when its ready during the year.
I hope that helps,, I might have confused myself. ;)