> on my end it wouldn't make any difference at all

Sure, but attribute (or tag) names refer the the structure of the document whereas values refer to each special case; structurally (essentially) those two are the same:

    <comment-box hackernews="1">
    <comment-box reddit="4">

but you can't tell because they have different attributes.

Okay, so in order to write (current solution):

    <comment-box hackernews="11850599" reddit="11850500 11859454"></comment-box>

you could do:

    <comment-box network="hackernews" items="11850599"></comment-box>
    <comment-box network="reddit" items="11850500 11859454"></comment-box>

which would work just the same, you just have to group consecutive comment-box into one; or you could even do this:

    <comment-box sources="hackernews: 11850599; reddit: 11850500 11859454"></comment-box>

(inline css style).