Do you think market(consumers) for GUI design software will increase or decrease in future? I do believe it will increase as more and more companies need in-house software. Also, it is worth noting QT has ~60 million dollars in revenue and that is definitely in the ballpark of VC backed money. You would probably have to deliver 10 million on a 1 million investment.
It mostly boils down to marketing and some quality of life improvements. Do you got a sales staff? Again, I'm in the gamedev business so I got no deep-down knowledge about GUI designer market but marketing costs are about 100% of development costs for desktop games (at the very very low end) and up to 1000% of development cost for mobile games. So in game development, marketing is the bulk of the cost, and development costs aren't all that important.
What do you think marketing costs are for GUI designers, or do you know how much QT spends on that? As an user I feel like Sciter is lacking good marketing at this stage but you can only know that and chart your way.
Please don't take any of the above advice too seriously because again I'm just a game developer, you will have to figure out this stuff yourself.