I feel like it's worth pointing out that since in C# you'll be able to target planets with beam weapons, being outranged in beam tech is actually something to worry about. Unless I'm misremembering how things will work, an enemy with longer range beams could park a beam ship just out of your range, and destroy your STO with its weaponry, with minimal damage to population and infrastructure.
It is possible, but as stated:
1) If you want to prevent sieges, build more orbital defense stations. Especially if you are out-teched. Do not let the enemy close if at all possible. I don't get this complaint about being outranged. Before, you had PDCs. Now, you're going to have orbital bases. It is the very SAME thing. You can put on your orbital defense bases the same things you had in your PDCs. They are functionally identical. So... what exactly is the problem with orbital defense bases?
2) As said by TCD, Steve's changes should mean that it's going to be very hard hitting troops who are heavily fortified and/or in rough terrain
3) As DEEPenergy said, failure rates. Supposedly, this constant bombardment will cost a TON of maintenance points, and cause a lot of failures. If this is combined to 2), that is if you're sieging a planet with rough terrain and a lot of fortified troops, it might take a long time and be very costly to bombard.
So it should all even out. And, once the orbital defenses have been destroyed, there should be a lot of situations where a ground invasion is just plain better.
... And also, I will be blunt. If you are out-teched and out-produced by an enemy who has a lot more ships than you, things ARE supposed to be hard. The state of the rules, as they should be, seem balanced enough for me.
If instead the place being attacked is an out-of-the-way planet and your forces are somewhere else, it's a case of being caught with your pants down.
And even more important, Steve did these changes to hit chances from orbit and to failure rates specifically to address these possible issues. Which means that if the numbers are not balanced, I imagine he will tinker with them until they are. I understand that a lot of mechanics are going to be very different and that can cause disconcert... but there's no need to be preemptively pessimistic in my opinion.