This is a rule of thumb I learned long time ago, in a totally different field of software development – “Every new release will slow the features affected by it by 10%”
Of course that was in the days when there were years between release and the figure of 10% was probably pulled straight from that person’s ***, but the underlying truth remains the same. You can not have more feature without hurting performance in some way.
So it should be trivial to claim that page generation with gutenberg will be slower as with addition to parsing shortcodes it will also need to introduce parsing its own comment markers.
The question that it is impossible to answer is by how much slower it will be. Most likely when it will be merged into core the answer will be “insignificant way” and (as always with wordpress sites) will depend more on your theme and plugins. In theory if gutenberg will enable you to remove some plugins, you might even gain performance.
(not even going here into caching as if you have a code page caching scheme, the difference in actual performance as a visitor sees it should be zero)