I have not heard about getting a cash offer to take a quarter delivery. Demand is so high now they will just assign the VIN to the next person in the queue.
Just so you know Tesla does not operate vehicles models by year refreshes as other car manufactures like Lexus, BMW, etc. When an improvement or modification is done they just change it in the line-up after reconfiguring the automation line. For example recently the MY and M3 had radar removed and moved to Tesla vision with the cameras on autopilot. This is why you see users here posting VIN information and it gives an idea of the built date.
A 2021 Model Y from Q1 this year would still have radar but will not include the heated steering wheel and other slight modifications since Q1. This is why many users in the Tesla community rely on the VIN and build date as the vehicle can be changed on several minor things during the entire year of production. Not all Teslas made the same year are equal. So waiting till 2022 hoping for next year's refresh does not happen the same way with Tesla.
The only upcoming change expected with the Model Y is the 4680 batteries Tesla has been developing. Outside of the expecting range and charging improvements we are not really expecting to see these batteries in MY or M3 until at least 2022. My wife asked me if I should wait to get the longer rumored range of 400+, but coming from a BMW i3 with a 75-mile range getting an MY LR now for 320+ is already a large upgrade. Unless it is a must for your needs for most users it is a minor reason to delay delivery.
I work in IT as a system admin and deal with tech changes daily. Tesla operates much the same way. Once you lock on a vehicle there are always R&D features being reviewed and applied to the vehicle that improves both hardware and software. While it is nice to get the new functions we need to ask ourselves does it really matter to us? It is a need or a want? Most of the features of the vehicle are software and once you receive your vehicle it will receive the free over-the-air updates that will continuously improve the car with enhancements and feature updates.