As Heise is reporting (German), the EU has already passed a directive to that effect, which will prohibit the sale of such devices from June of 2016.
Both regulations require manufacturers to include effective measures that only allow firmware to boot on the device that has been signed by the vendor. If the device is lacking such protections, it cannot be sold anymore. Given that the FCC and EU regulations cover a large percentage of the worldwide market, it seems reasonable to assume that all vendors will only sell such limited models even in countries where it's not required, instead of developing two separate models.
This will curtail custom firmware and open source software efforts to a massive extent, so I'm hoping this community as well as others (DD-WRT, OpenWrt, etc.) will be able to persuade politicians to change these rules before the come into effect.
For the US. the FCC is accepting comments until September 8th.