an additional linecard is still several k$, money which could be better spent
on more servers, i think.

Fair enough, I didn't think to would be that expensive, $100 at most.

over the next few months some changes will be made to the network setup at
knams, which might make it easier to provide some additional redundancy without
spending so much (because we will no longer connect the entire toolserver to
the main Wikimedia switch).

Sounds good. Thanks for the clarification

Simon