Thank you for being considerate in your request for us to be considerate to your wishes for the game. A nice change of pace from all of the ankle-biting and crying that everyone else has been doing.
The issue with making the difficulty selective in one mode and not the other, I.E. making Solo play variable in difficulty and Open the same difficulty for everyone, is that you only have one save shared between all of them.
This means that it's exploitable by people who don't want to work for their rewards, and they will use it to circumvent penalties in Open Play that wouldn't exist in Solo. I'll provide some examples.
First and most obvious: I play in Open but in Open money is harder to earn than in Solo since the theoretical new changes to Solo which have introduced an Easy difficulty. If I see something I want added to the game that's going to take me a significant amount of time to earn money for, I could go to Solo, set it to easy, and earn that reward in a fraction of the amount of time it would take me to earn it in Open, then skip back to Open and I would have an advantage over everyone who decided to stay and play in Open since I keep my rewards. This will result in a trend where everyone starts dropping out of Open to earn credits, reputation and materials at the faster rate because they don't want to be disadvantaged against anyone else who also does this.
Edit: I forgot to include more than one example... OOPS.
Secondly, I could do the same with reputation, earning it in Solo faster than in Open.
Thirdly, I could do it to fix my mistakes without having to worry about the penalties of those mistakes. Say I get a bad reputation with a faction and that faction becomes hostile, while I'm deep in their territory. I can log in to Solo, change the difficulty to easy and leave their territory much more easily than I could by staying in open, on top of being able to change my reputation back to friendly faster and easier by doing the required tasks in Solo.
The immediate response to this is to make Commander save files separate for each instance: Open, Solo and Private. Sadly this idea has been rejected by both the devs and the community, and for good reason. From a technical standpoint the game is not in a great position, and there are often times when Open play is not functioning. During these times Open players have to date been able to drop to Solo or Private to continue playing, but unique saves between all of the play modes would be a huge detriment to what has been a saving grace for many players in the face of FDev's continued technical problems with their server structure, especially in the United States.
There have been hundreds of pages of discussion on this topic scattered about, in different places and times. It is the proverbial dead horse. There are also significant issues that would arise with some of the game's core design choices regarding the implementation of any type of adjustable difficulty, mainly that it would require a complete rework of how the Non Player Characters work, and that those changes would be so significant that many of the game's other mechanics would have to be changed to fit with them.
Feel free to continue asking questions and making suggestions though. we always enjoy the input when it's well thought out and presented politely. Sadly this is almost never the case with the rest of the community.
On a final note I'd like to point out a maxim that has been true about game design since man decided to waste his time playing them, going back to skipping stones and rolling dice.
If you cater to everyone, you satisfy no one.
