IMO Tesla not being more specific now about future battery replacement costs should not deter potential buyers once they learn about the warranty and how packs on high mileage Teslas are holding up. A conversation with a potential customer who asks about battery replacement cost might go like this.
Customer: How long will the battery pack last before I need to replace it and how much will it cost ?
Sales Rep: Many Teslas sold years ago have been driven over 300,000 miles and their battery packs have 75% or more of original capacity and are still going strong. Model 3 and Model Y battery packs are even better and will last even longer. Tesla battery packs are warrantied to have more than 70% of original capacity after 8 years, no matter how many miles you drive. Most owners may never need to replace the battery pack. Today the pack is about 20% the total cost of your car. But batteries cost less to make every year, so we expect a replacement pack 10 years from now should cost half or less what your original pack does today and have even greater range.
The "no matter how many miles you drive" part only applies to the Model S&X. The Model 3 has a limit of 100k/120k on the battery warranty. I don't think we know the warranty details for the Model Y, Roadster, or Cybertruck yet.