Here’s my thought on it. Since two sparks are required to make a mythic, it would be fair that two sparks are required to add a GA to a piece of mythic gear. But let’s take it a step or two further. The same way we have legendary aspects, we should also have unique and mythic aspects that can be improved. Additionally, being able to make a really good legendary into a unique, and a unique into a mythic, and being able add or reroll a GA would significantly enhance gameplay. The biggest issue with gear isn’t overall quality, but the lack of deterministic crafting. The lack of flexibility of being able to craft gear to your own specs like in POE is what is making the gear bland. It prevents you from being able to fully theory craft gear for unique builds and play styles. Additionally, being able to craft your own mythics and augment them with tempers and such would seriously elevate the game. In this way, no two people will necessarily have the same game experience. It’s more tailored to the player’s individual tastes and gives them more control over the kind of game they want to play. Hunting certain mobs or bosses for crafting mats that can only be obtained from them will do more for the overall game experience than anything else that has been implemented.
Furthermore, the seasonal abilities that a character has should either be permanent to that character, or be an option that you can choose from a menu, so with different builds you can continue to experiment and explore the game in different ways. This will stimulate consistent gameplay in the off-season so eternal gameplay has a purpose.
The biggest issue the game has is a lack of flexibility in gameplay due to the static nature of gear, the overall lack of crafting, and the constant overcorrections with “balancing”. If something works, leave it alone. Let people enjoy what they want to enjoy in the way they want to enjoy it. If you have to break something to make something else stand out, you’re doing something wrong.
And last but not least, bring back Set Gear. It would bring a whole new dynamic to the game which was a fan favorite in D3. Going bonkers with stupid high damage and crazy proc interactions is what made that game awesome. These simple changes would transform the game in a way that would increase the player base by 300%. The lack of quality options and being able to build your character the way YOU want it to be is what makes the game stale as a whole. These are very simple quality of life changes that would bring everyone’s experience to a whole new level.