Did you read this at all? FiveM Support For Newly Announced Grand Theft Auto V Upgrade Coming Soon
It tells you exactly how it will work and no one expected this to be a “DLC”. Servers can choose which version to run which will determine which version you need to have installed. The only “DLC” like part is you will get access to cars previously only available on console.
This update will do nothing to optimize any existing scripts or resources. It is almost completely graphical updates. Servers that are not already optimized will become worse if they force the enhanced edition. To my knowledge, there are no major RAGE overhauls that add a ton of extra options.
Any technical improvements are related to using more modern features like direct storage, ray tracing, DLSS/FSR, etc.