Classic flat planet?

This is one of the reasons I like the pick your landing spot philosophy.

Care to share any further details on how you see such a mechanic working in practice?
i.e. Things like how to mitigate the rather obvious risk of opposing players choosing spots too close to each other.

It would be fun if that wouldn't matter for the balance. Happen to start real close to each other? You better be able to use your commander offensively.
Imagine a game where both commanders start in range of eachother and keep fighting all the game until they blow up the planet.
Although a big death explosion would likely make those games result in a draw.

Total Annihilation Kingdoms have one of the most interesting duels between coms(monarchs) which can last all the way from the beginning to the end of the game.

Although an easy solution if people dislike com duels or close starts is to restrict the placement to say 25% of the north side of the planet while the other player get 25% of the south side of the planet.

Zero-K has a system which would be perfectly usable here - players choose where to 'land' their commander, and each team has a zone to land in. The host can choose how big the zone is and where on the map it is located.

In a 1v1 scenario, you could very easily split a planet in half with a small buffer zone between zones, and players can then choose where on the planet they land.

Add in automatic resource generation that is dependent on the player's location, (ie, no player gets 'lucky' because the resources are evenly spread out based on where the player is, not the map) and you've got a winner.

Since this thread has been abducted anyway: i think a two staged approach would be the most fun: Select a starting point, within certain map specific parameters of course, like on a specific body only. Your rocket will then fly there, this is visible for the other players as to avoid hide and seek type scenarios. Once You reach your destination you stay suspended under your hovering egg and you have a specific amount of time to move around, this can also be variable per map. Once this time is over all players are dropped and can start building.