Sins of a Solar Empire has been apparently doing very well over the past few years. Rebellion has even had an excellent DLC, and the support continues to be fantastic (The recent patch beta is an example). Obviously, fans of the game are eagerly awaiting news from Ironclad or Stardock, perhaps in 2014, about Sins of a Solar Empire II. I would like to share a few of my ideas, and will do so early, before the game design is finalized. I think that by the time a game is announced, it is often too late to provide feedback on the game design, as that phase is over.
I have tried not to excessively duplicate the ideas of others, but I may have missed a few things in my forum searches. Here are the first two ideas:
1. Make planets a more important part of the game by giving them extensive specialization options, similar to what starbases have now.
The additional planet specialization paths were one of the reasons I was so excited by Forbidden Worlds. Although planets now have a significant number of puchasable upgrades, they are rather uninteresting. I think the main problem is that all the upgrades except the culture/industrial specialization have no reason except cost for you not to purchase them. In other words, there is no opportunity cost to upgrading your population, except the loss of resources which you plan to make up in additional tax revenue. The culture and industrial specialization at least require you to make a choice, so that is a step in the right direction.
I envision a system similar to the current system of starbase upgrades. Each planet would have a certain number of upgrade slots, and most planet upgrades would take an upgrade slot, or possibly two for a good upgrade. Multi-level upgrades are also exciting. Different planet types would have different numbers of upgrade slots, and also different possible upgrades. Possibly some upgrades, such as Emergency Facilities, would retain their current implementation and not require upgrade slots, as that might be a little unfair for defensively minded players. Logistic/Tactical slots could also remain as it is now.
One benefit of this system would be an easy way to increase planet diversity. Asteroids could have three upgrade slots, Desert planet could have 9, etc... The cultural specialization upgrade would not be available on barren planets, Ferrus planets would have a special unique upgrade (Advanced Metal strip mines, perhaps?) that reduces metal costs of ships built at that planet, etc... Most planets should have different combinations of upgrades available. Perhaps only the most important will be shared by more than two of three planet types. The possibilities are endless!
As an example, consider a small planet your empire has recently aquired, a forest planet with 4 upgrade slots. You could build an exotic woodcrafting facility, boosting trade and allegiance of planets within two jumps that have a trade port. However, you are on the warpath and need more capital ships, so you could build a fleet academy to train capital ship crews (See idea #2). You could go the economic route with population upgrades, an upgrade to your refineries within one jump (+20% refinery income, stacks twice), or an economic development center, which decreases cost and increases research rate of economic upgrades. If you want to fortify your planet, you could build "D-band Deep Space Target Aquisition Radar", which increases range of tactical defenses by 50% (Not starbases), level 2 also increases range of friendly ships by 20%. Possibly your frigate factories need an "Advanced Engineering" upgrade in order to produce advanced cruiser types.
You will have to make your choice wisely, as your options are limited, but there should be an option to scrap upgrades after you have purchased them if you change your mind (you lose most of your money, of course).
2. Remove or relax hard limits to the number of large ships (capital ships/titans) players can build at one time.
Think about this situation: you, have a large empire of about forty planets, in three star systems (and, with Sins 2 awesomeness, there is no singleplayer lag!), but can only field one Titan, and 16 capital ships (these numbers might be changed but the point stands), which is the same limit for the puny empire with four planets that you are invading. Your empire is fighting a four front war in these three systems, and you are trying to cobble together an invasion fleet to invade a fourth system, but frustration is building as you can only fill most of these fleets with frigates, cruisers, and very few capitals.
Of course, I am not suggesting that all limits other than fleet supply be abolished. (More on fleet supply in another post...) Having significant requirements for the larger ships beyond what is required for frigates/cruisers is not a bad idea. There are a few ways to do this without crippling large empires. One simple (and inelegant) solution is to use a system similar to the current system for superweapons (I think?), where only one can be built for every four planets that your empire has colonized. This would work out to having a second Titan become available when your empire colonizes 10 planets (Titans could still require cap ship crews), for example. Capital ship crews could also be trained in special facilities on planets (See idea #1), instead of the current static research system.
The only thing that would be really important is ballancing the larger ships so they do not become too powerful (or possibly underpowered). This is a good idea in any event, even when you can only build one.

Links to other posts in the series:
Part 2