I'd like to know if it's possible that, although you may download now and install Odoo v8 under AGPL, this can change in the future for v8 or whether any change in licensing would just apply to future versions (v10 for example). Thanks for any clarification on this.
The founder and president of Odoo Fabien had removed own tweet on 26th May, ~2011.
"Tweet was: OpenERP will always remain AGPL. We have a way to satisfy customers and partners demand without dual-licencing." .
Odoo has the right to change the licensing at any time however the founder and president of Odoo Fabien has stated many many times that that will not happen.
Is there something specific you are concerned about?
I just noticed that you said pay a license in 5 years to use v8. That could never happen. V8 has been released with the AGPL license. This license can never change. They can only change a license of a future version of odoo. So if you download a copy of v8 today you can use it until comets destroy the earth or you want to upgrade.