How wide/narrow do we want these proposals to be?
Most coins (LTC, ZEC, DASH, etc) are forked from Bitcoin code and therefore will generate questions best suited for Bitcoin Stack Exchange
Ethereum forks and DAPPs such as Golem, Digix, and Gnosis can be asked about on Ethereum Stack Exchange
Monero forks like AEON and related projects such as Kovri and OpenAlias belong on Monero Stack Exchange
The blockchain proposal scope seems more appropriate than the cryptocurrency proposal because it covers general blockchain topics that are not specific to one cryptocurrency (most of which already fit within the 3 existing SE sites above.
As currently worded, the only coins that are appropriate for this cryptocurrency proposal are projects not forked from (or DAPPS designed to use) Bitcoin, Ethereum or Monero. A few relevant examples include NXT, XRP, SC and MAID