Depends on what you mean by level of support. If you mean hardware, it will never get USB3 or display out. This will make it less attractive as a linux phone, which means it will get less support from the tinkerers.

If you mean community support, after reading a few topics on the Fairphone forums, probably never. To put it in perspective, I know I wouldn't accept a hypothetical free FP5 to FP6 upgrade.