How do I limit entries retrieved except those with a sticky lightswitch on the entry?
One method is to check to see if item is not in array before merging. The downside is that the entries will just be appended vs sorted by meetingDate.

{% set stuck = craft.entries.section('meetings').relatedTo(subcategory).sticky('1').order('meetingDate desc').find() %}
{% set entries = craft.entries.section('meetings').relatedTo(subcategory).order('meetingDate desc').limit(2).find() %}

{% for stuckEntry in stuck %}
    {% if stuckEntry not in entries %}
        {% set entries = entries|merge([stuckEntry]) %}
    {% endif %}
{% endfor %}


The other method is to grab the ids from the 2 queries and then merge them together, and perform a new query which can be sorted.

{% set stuckIds = craft.entries.section('meetings').relatedTo(subcategory).sticky('1').ids() %}
{% set entryIds = craft.entries.section('meetings').relatedTo(subcategory).limit(2).ids() %}

{% for id in stuckIds %}
    {% if id not in entryIds %}
        {% set entryIds = entryIds|merge([id]) %}
    {% endif %}
{% endfor %}

{% set entries = craft.entries.id(entryIds).order('meetingDate desc') %}