void nothrowStuff() nothrow {}
void pureStuff() pure {}
void stuff() {}

auto funcPtr = (0 == 0) ? &stuff : &nothrowStuff;
auto funcPtr2 = (0 == 0) ? &stuff : &pureStuff;

test.d(5): Error: incompatible types for ((& stuff) ? (& nothrowStuff)): 'void function()' and 'void function() nothrow'
test.d(6): Error: incompatible types for ((& stuff) ? (& pureStuff)): 'void function()' and 'void function() pure'

void function() pure and void function() nothrow should be considered subtypes of void function().  A void function() pure or a void function() nothrow simply provides an extra guarantee not present for void function() and thus can be substituted in any context for a void function().