There WILL be quality issues with Model 3, that is a given. Tesla is not known for its quality manufacturing and QC has been an ongoing problem for the last 4+ years since Model S went into production. Today's Model S rolling off the line has more squeaks, rattles, and fit and finish issues than my 2013 pre-Autopilot Model S. I believe this is due to Tesla's upper management, aka Elon Musk, pushing for higher deliveries, therefore pushing QC issues to owners and service downstream.
While I have a Model 3 on pre-order, I am not looking forward to the first generation issues that vehicle is going to have. Furthermore, has anyone heard of Tesla testing the Model 3 anywhere but California? This is cause for concern, in my opinion, as California does not represent all of the weather climates where Model 3 will be sold. Other vehicle manufacturers thoroughly test their cars in all kinds of climates - subzero, desert, humid, etc. Yet Tesla seems to think its adequate to test Model 3 in and around Palo Alto. I believe this may come back to bite early owners in the ass, especially when it comes to issues in extremely cold, snowy, and damp climates.
If you think Tesla vehicles have a better build quality than BMW, I'm here to tell you that's not the case. Service, on the other hand, is first rate and they have always taken care of me. But in terms of initial quality, Tesla sucks. Model 3 will have an entirely new drive train design. Ask early Model S owners how that's worked out for them. I have gone through four drive train replacements in the four years I've owned the car.
For those who are adding themselves to the wait list now, I think the next two years while you wait for your car will allow for a lot of issues and bugs to be worked out. Tesla will likely also update the vehicle significantly within the first year to higher performance variants that will likely include improved technology.
Based on Tesla's track record, I would say expect quality problems, expect a lot of time in service, and expect plenty of communication issues...
ON THE OTHER HAND!
After having said the above, am I canceling my Model 3 reservation? NO.
Would I buy another Tesla again based on my experience? YES.
The cars are so much fun to drive that the negatives fade into the background noise after a little while.