The Czech company (I think its actually a non-profit) that operates the .cz TLD apparently also makes routers.
They crowdfunded a normal router in the past, the Turris Omnia, there was a thread about this, but their second project is a modular router design spread across multiple boards that plug together.
I forgot to post this earlier, so now it is actually fully funded, but it looks like you can still pre-order units.
|A||1 × CPU
1 × microSD slot
1 × USB 3.0
1 × Gb Ethernet
|CPU is a Marvell Armada 3720 1,2 GHz dual core
Ethernet port is PoE ready
|B||1 × mPCIe slot
1 × SIM slot
|Examples given: LTE, WiFi, or SSD|
|C||4 × Gb Ethernet|
|D||1 × SFP connector cage||up to 2.5 Gb/s|
|E||8 × Gb Ethernet|
|F||4 × USB 3.0|
|G||1 × mPCIe slot|
There are of course restrictions on how many of each card. For example, you cannot have more than one A, B, C, D, or F module. Some cannot be used together, like B/F or C/D.
Still, it looks like an interesting idea to me.
Meta Question, is this thread fine in Networking/Hardware or since it is more consumer-targeted would it belong in Hardware/Other?