This is just based on my limited personal info and contacts. I still get that message and have not yet filed 2019. One of my clients was having problems until this weekend. They qualified for stimulus and have filed both, but could not get to the bank info due to various errors, but finally this weekend they got notice that their check will be mailed next Friday.  My daughter in law has not yet filed 2019 and received her direct deposit last week. My guess is, based on limited data, is that all 2018 stimulus payments are "in the works". I THINK they are sending to the lowest income first and working their way up to those that are probably closer to the break even point later. 

My understanding is that the stimulus money is not to be used to offset anything. I do not believe filing a tax due return now will delay anything, but it will not get their deposit information in any quicker. Personally I sent in an extension payment to overpay my taxes, so when I do file (probably next week) I will get a refund (small), but I can give them my bank info.  People First - https://www.irs.gov/newsroom/irs-unveils-new-people-first-initiative-covid-19-effort-temporarily-adj...

My suggestion is to tell them to google the question so that you don't give them the wrong answer. This new moving target is way to hard to out guess and actually way beyond what our tax "preparation" is supposed to go.  Or just say "I wish I knew. I am not sure even IRS or Mnuchin knows."

They can file now, but payment is not due until 7/15.