In short, no different from you accepting only rubles, and me having only pesos. This sounds like the worst of both worlds, no?
Eh, no. Because the issue is pretty much solvable.
Not seeing the difference. I'll quote your 'solutions,' and show that they are identical to using different fiat currencies:
1) I use an exchange account for deposits of coins that I do not regularly receive, so you do nothing but send your LTC or DOGE. I then convert those to DASH which I accept and withdraw them.
We use Forex.
2) You first convert your LTC or DOGE to DASH which I accept, in some exchange, and send them to me.
I convert my pesos to rubles, send them to you.
3) We use a payment processor
We use a payment processor.
Where's the difference?
Also, in all the options you have offered, how does Bitcoin factor in?
First, most cryptocurrencies are based on the bitcoin protocol. So bitcoin is still in use, as a protocol, even if it isn't as a currency for a particular transaction.
If I use LTC, I still use the bitcoin protocol. The elements are pretty much the same.
I see. So if no one uses the BTC bloccahin, and everyone uses LTC, we're still all using Bitcoin, correct?
Second, in some of the options, like having an exchange account, you can either use BTC, or not.
You mean I could first trade my cryptopesos into BTC, pay fee, then convert that BTC into your cryptorubles, pay fee again, and give you the cryptorubles?
Why would I do that?
For example you can accept 100 different altcoins and have it set to be converted to BTC on arrival and then make 1 fat BTC withdrawal in the end of the day (if you are a merchant). So you might have gotten paid for 300 coffees with DOGE, these money go to the payment processor or exchange, and in the end of the day you get, say, 2 BTC.
But why involve Bitcoin at all? If [crypto]rubles is your chain of choice, why not have the exchange convert all the small transactions directly into cryptorubles, and, at the end of the day, withdraw it in a single transaction?
How would that work?
Code-wise it shouldn't be that difficult. It might be a lot of work but in essence it is a decentralized asset exchange, specifically for cryptocurrencies/altcoins, merging functionalities of different wallets in order to transact in multiple blockchains.
Who is running this "decentralized exchange'? What's the incentive? How many nodes? All the nodes will need to have copies of each and every blockchain, no? You think that is a trivial coding problem?!
Your 'decentralized exchange' sounds like an uber-complex cryptocurrency in itself. Why not simplify it significantly by having it issue its own tokens?