I am an Indian, and very few among us can claim that they know the length and breadth of India. Foreign journos who call themselves experts of India are just kidding themselves.
The history of caste itself has a different origin. Caste was designed as a way to organize people back 5000 years when humans weren't even having proper clothes. So you are born, you are tested, and some people decide you are good for this job, and they are assigned to that caste. Very similar to English last names like Wood, Butcher, Cook, Green etc which are nothing but names related to their work done by their anchestors.
Now that system evolved into based on birth, and to preserve the power of ruling and priestly class, wrote some Hindu texts to suit the narrative and gave it religious sanction. Now my English equivalent of my caste is Potter. My anchestors used to be clay pot makers. My great grandma father switched to Agriculture, my dad a teacher and me electronics engineer.
Technically, let's say you are a foreigner, and if.you convert, you can convert to a Brahmin. No religious sanction is required. I think Arya Samaj just converts without giving a caste tag. All castes have like 60-70% of similar customs. But castes have their own distinguishing customs. Like the way one gets married, costumes, burial rituals etc. So if you are impressed by a caste customs, you could get into that, but you won't receive a official certificate for.the same except having the name Hindu on your religious certificate.
It's so exhausting even to type for me. Indian govt has institutionalised caste for administrative purposes. For reservations as example. And I just explained not even 1% of differences. Hindu God's are separate from.castes. Shiva or Vishnu or Shakthi are worshipped by all across Hindus, across castes. And that is what BJP or Hindutva project is in India. To unite people like Abrahamic religions and to get them above their caste identity. Detractors say this is an attempt by High caste Hindus to subsume lower castes so they can maintain their hierarchy. While I find merit in both approaches, people following the second approach has never really tried to abolish castes in the first place but try to use castes to drive more wedges among castes.
Good thing, people have changed a lot. Inter castes marriages are rising across India (including me who got married like 4 months ago
) and as time goes on, caste discrimination will go less.
As for relationship btw Dalits and Muslims, it's a Mirage of alliance of convenience in my opinion. And I can only talk of my limited experience. Different Indian states have different ground realities on going. I prefer to use the word SC for Dalits as I find the word "labelling". SC in the largest Indian state of UP are hardcore voters of BJP. The so called alliance btw SC and Muslims is nearly nil. Communal clashes have taken place btw Muslims and SCs too. But SCs are being wooed upon by upper castes to build a larger Hindu conciousness. And I think SCs would find appealing of Hindu conciousness than Muslim alliance. Cos Hindu conciousness takes their distinct cultural practises into account. Muslims don't, expect uniformity and don't make compromises. At the end of the day SCs are kaffirs. And that wouldn't make an alliance a long term options.
SC leaders have tried, still trying to stitch an alliance. In some states it's partially successfull. But I don't see an long term alliance coming out of it.