How did you get into it? I think something like that would be my dream job. Yeah, I'm not normal :)
I used to work as a scientific/medical translator and one of the things I loved about my work then was that with each new project, I had to learn enough about a new topic/subfield to become a bit of an pseudo-expert in it. I greatly enjoyed that research and would love to do some work in software development that would require the same type of constant learning with each new project. Diving into some convoluted, 20-year-old Fortran driving highly-specialized scientific software actually sounds kind of exciting to me (yeah, I'm not normal either :) ).
Is there much demand for this kind of work, I wonder? I'm guessing the best way to get your foot in the door is to be in academia, and those days are long passed for me.
As an undergrad, I had a good friend who was doing his PhD in Atmospheric Physics. It turns out, most of that field works in Fortran '88. This is not a very useful language, seeing as it uses GOTO statements to function as a loop. Fortunately, it does have comments. My friend managed to sweet-talk an older PI into giving him the old code for use in nuclear blast atmospherics (Exp: say you nuked all of France, what happens to Greenland's ice). At about 3 am before a project was due in the morning, he was pulling through the spaghetti that was the code, tired, jittery, and over-caffeinated. In this mess of logic diagrams he had to draw out by hand, he finally got to somewhere he thought was going to really cement all the code together for him. He follows a GOTO statement, and there was only a set of another GOTO statements. This went on for about 30 (my recollection of his words) GOTO statements, all 'nested'. Eventually, he gets to one that only has a comment line: 'HAHA MADE YOU LOOK'.
His laptop was defenestrated and he had to buy a new one with me about a week later.
You can staff projects off of grants, so it removes the need to sell the product. And the companies are probably going to be more academic, with a high percentage having graduate degrees. But companies will be under pressure to win grants. And because they have less of a need to sell a product, your work might not be widely used after the project ends. Also, the DoD is a major source of grants, so it would be helpful if you were comfortable with working on military research projects.
But it might be something to look into if you want to get into software development in an academic environment.
Academia is being pushed more and more toward industry collaboration, so if you can get the exposure and connections it shouldn't be too hard to find the opportunities from the inside.
You really have to enjoy this kind of work and some of the frustrations that come with it. I did, but ultimately had to leave when funding for my group ran out. If life circumstances allowed me to work for less I might have stayed with them.