This thread is getting hard to follow. There seem to be various mixups going on.
p2pool is an alt chain of its own and it has miners. Bitcoin nodes don't mine though.
Altchain is better terminology than altcoin. It is like subordinate chain or side chain, but ultimately pays in the coin of the mainchain.
"nodes don't mine" is more or less temporary. After few more knees on the distribution curve the incentives will align more toward propagating transactions instead of trying to snipe the coinbase with a small block.
This is incorrect. Although, you can't incentivize the process of just running a node, you have to incentivize both the speed and volume of the process of tx propagation.
I think that this opinion seems to miss the that there are two p2p protocols within the Bitcoin network:
a) real-time transaction and block propagation network
b) historical block synchronization network
Currently they are awkwardly rolled into a single p2p protocol, with a branch appearing fairly recently "relay network" that concentrates on task (a). The task (b) is currently badly served by the original legacy protocol. Sooner or later the Bitconin developers will understand that they need to import more features from the well developed bulk transfer protocols like Bittorrent and maybe even from paid on-demand streaming. "headers first" isn't a real solution, more of a temporary workaround. Certainly it doesn't subsume the bulk-transfer functionality of a better-engineered protocol like bittorrent.
Why altcoin? It is more like p2ppool, but instead of shares for mining one would get shares for proven transaction propagation.
That's a bit hard to do when their are things like
pseudonode.
Pseudonode cheats only on the task (b) above, I think it does decent job for task (a). Other than this I don't really understand the above comment.
The current situation in the Bitcoin brain trust is that almost everyone suffers from some sort of brain constipation about how to change a single line of code
static const unsigned int MAX_BLOCK_SIZE = 1000000;
Ultimately this problem is going to solve itself in some way and people will again resume working on other long-term issues.