Both have been their own modes as limited-time Events.
In general, diluting the playerbase across a wide variety of different matchmaking queues results in longer wait times. We have 10 tiers of ships in our game, as well as Superships, so even just having a single mode can result in a lot of different queues as people split due to the variety of choices available. Random Battles and Co-Op offer support for all-tiers, which is already a large amount of options. Adding more modes makes for further dilution.