I agree that more question types for the Quiz module would be a good investment. I think looking into the "science of learning" (SoL), which has been having a renaissance over the past couple of decades, could provide inspiration for some evidence-informed designs.
For example, I tried stirring up some interest in a variation on cloze deletion tests (among the most valid & reliable reading comprehension & language proficiency tests available), called the "c-test" here: https://moodle.org/mod/forum/discuss.php?d=404858 It's a simple algorithm that generates the tests from any text you can copy & paste into it. That makes it easy generate valid, & reliable assessments quickly & easily. However, it's still not feasible in Moodle & I'm currently still sacrificing trees to print paper copies of c-tests for students. The nearest question type is the Embedded cloze (See: https://docs.moodle.org/404/en/Question_types#Embedded_Answers_(Cloze_Test_/_Gap_Fill)) but it's a painstaking process to create even short c-tests with it & even then, the results are less than optimal.
The main thing that Quiz question types can be useful for is "retrieval practice," i.e. strengthening ideas, concepts, vocabulary, etc., in learners' memories (e.g. See: https://www.retrievalpractice.org/ & https://www.learningscientists.org/). Many of the existing core Moodle question types are excellent for this & GIFT & other authoring formats make it relatively easy to streamline the process of authoring & uploading large numbers questions into question banks.
Re: GUI designs, I see this as time & effort well spent. A clean, logical, easy to navigate LMS is essential for helping learners to focus on the learning content & not distracting them with irrelevant features. Ignoring distractions takes cognitive effort, which in turn, reduces the cognitive capacity that's available for processing (thinking hard about) learning content. Managing cognitive load within the demands of learning resources & activities is one of the most consequential aspects of learning efficacy/efficiency (See: https://en.wikipedia.org/wiki/Cognitive_load). An optimal GUI for learning, i.e. thinking long & hard about things, is pretty much the opposite of commercial sites like Amazon, Facebook, Youtube, & Tiktok, i.e. not thinking & just reacting/responding to stimuli, like rats in a Skinner box (What they really want you to do is click on the ads!).
Personally, I'd like to see Moodle GUI development & Activity design go in more evidence-informed directions rather than simply following popular demand; remember that the learning styles myth is still very popular among educators! 😬