That sounds like a neat addition to the game! Creating a simple TMR feed mixer that allows players to use hay, silage, mineral feed, and possibly straw to produce TMR is a great idea. It adds another layer of realism to the farming experience and allows players to manage their livestock more effectively.
Having the ability to craft something functional from the resources available is a core aspect of farming and can be quite rewarding in-game. It also encourages players to think creatively and make the most out of the resources at hand.
Allowing players to place the feed mixer on their farms adds to the customization aspect of the game, giving them more control over their operations. It also adds a sense of immersion, as players can visually see the process of creating TMR for their livestock.
Overall, introducing this feed mixer in a beta version could be a fun and engaging feature for players to test out and provide feedback on. It adds another dimension to the gameplay experience and opens up opportunities for further expansion and customization in the future.