This is already supported. See below.

[subbu@subbu-wmf tests] echo "* foo <li> bar" | node parse --normalize

<ul>
<li>foo</li>
<li>bar</li>
</ul>

[subbu@subbu-wmf tests] echo "* '''[[Power-to-weight ratio|Power/mass]]:''' 0.034 hp/lb (0.056 kW/kg)<li>'''[[Lift-to-drag ratio]]:''' 11.9</ul><big></ul>'''Armament'''</big><br/>" | node parse --normalize

<ul>
<li><b><a href="Power-to-weight_ratio" title="Power-to-weight ratio">Power/mass</a>:</b> 0.034 hp/lb (0.056 kW/kg)</li>
<li><b><a href="Lift-to-drag_ratio" title="Lift-to-drag ratio">Lift-to-drag ratio</a>:</b> 11.9</li>
</ul>
<big></big>
<p><big><b>Armament</b></big><br/></p>

Well, I'm not sure what's the expected HTML output, but the URL doesn't look pretty.

Ah I see what you mean ... I was about to say that http://parsoid-lb.eqiad.wikimedia.org/enwiki/Consolidated_PBY_Catalina?oldid=326925504 looks pretty enough to me.

I'll have to take a larger piece of wikitext from that area and investigate. One of us will in the coming days. This feels slightly lower priority compared to the other brokenness we have to fix.

One option would be to fix up the wikitext to be less broken than it is and see what it fixes.

<big></ul>..</big> should instead be </ul><big>...</big>

Sure, this looks rare and it's not tragic.

From https://en.wikipedia.org/w/index.php?title=Template:Aircraft_specifications&action=edit

...
}}<big>{{{armament header|</ul>'''Armament'''}}}</big><br/>
...

Not sure if there is a way to fix that. I am lazy to lookup the exact parser function syntax, but the wikitext equivalent of:

if ({{{armament header}}}) {

<big>{{{armament header}}}</big>

} else {

</ul><big>'''Armament'''</big>

}<br/>