Anybody have any new news on this?? The BIOS has not been updated for this and for that matter hasn't been updated in over 2 years. Quite frankly, I would say that the chances of R4/5 BIOS support for rebar being added now or in the future is less than 0.1% chance. And that .1% chance, IMHO, is only if the rebar update gets gratuitously added during the driver updates for Windows 11, since Dell has stated it will test the R4/5 for upgrade to Windows 11. Keep in mind that you'd need to have an aftermarket GPU though to support rebar. No OEM GPU that shipped with the R4/5 would meet the requirements for rebar. Anyway, if you wanted to keep on top of it you can periodically check their driver page for new BIOS updates.  drivers and supported models listed by said drivers that Nvidia Resizable BAR would only be tested/validated for the   Aurora R10/11/12 desktops. DELL-Chris M>   
There has been enough silence on this subject. I am a 2017 Area-51 R4 owner and was hyped to see that manufactures were providing support for Nvidia Resizable BAR on Intel X299 chipset platforms. Surely Alienware would follow if the demand is high right? EVGA Enables Resizable BAR Support on X299, Z590, & Z490 Motherboards | TechPowerUp MSI Offers Resizable BAR Support Across All HEDT Motherboards Including AMD TRX40, X399 & Intel X299 (wccftech.com)
Area-51 R4, Resizable BAR for X299 chipset!