The Redmi Note 4 was indeed a very popular phone at its time due to its solid performance and competitive pricing. Compared to today's mid-range phones, it won't measure up in terms of processing power, camera quality, or display technology, as these areas have significantly improved over the years. However, it can definitely still serve as a viable option for repurposing.
Using it as a dedicated music player is quite feasible, especially if you install a lightweight music app and possibly pair it with a good set of Bluetooth headphones. To enhance its performance for this purpose, you might consider performing a factory reset to clear any old data and installing a custom ROM designed for efficiency and minimal resource usage.
As a smart home controller, it can handle basic tasks, especially if apps like Google Home or similar are compatible. It might not support the latest smart home tech, but for simpler setups, it should work fine.
For specific mods, rooting the device can unlock additional customization options, though this does come with some risks, such as voiding warranties or bricking the device. Make sure to back up your data first.
Overall, it's still a capable device for specific, non-intensive roles. Just remember that battery wear might be a factor if you haven't used it in a while, so consider replacing the battery if needed.