When you live long enough it becomes evident that scale in tech is a pandemic. At a certain point greed inevitably takes over. I believe there's some kind of a threshold beyond which a company has no choice, but to turn evil.
It is not necessarily evil, but corporate interest led.
When it was created, gitlab core value was to be the open source alternative to GitHub.
Then, it started to add light premium features.
Now, free versions have a lot of frustratingly limited features with nag screens to push you to subscribe.
The free core is less and less a priority and less and less sufficient.
After the ipo, things will get even worse. Most of new shareholders (Ie owners) are just profit led. It's an investment for them and they will want the net result to grow at whatever cost.
Management has no choice else than to follow what shareholders require.
So, if it is economically viable, nothing prevent gitlab to stop new versions to be open source if they think that will make them more profitable.