Hi Martin,
I'm on the road at the moment with a similar goal; getting to India. I'm currently in eastern turkey. With the recent closure of the Wagah border my plan to go through Pakistan had to be changed. So now the options i had/have would be either Iran > Turkmenistan > other stans/Kyrgyzstan > China > Nepal > India, or Georgia > Russia > Kazakhstan > other stans/Kyrgyzstan > China > Nepal.
Turkmenistan is a pain in the back to get a transit visa. You need to book a tour etc. I met people doing this. Its not impossible but you better figure this out way in advance. There is no "get to the border and see" around these parts, not at the moment anyway. Turkmen embassy in Ankara is a shitshow.
Then there is some options to go through Afghanistan. Definetly possible. There is no foreign embassies there to most western countries so if youre there and you run into trouble thats on you. I didn't look too much into this, but if you were to go to Afghanistan you might want to organise this in advance as well or risk getting turned back. From the information I found there are few embassies to Afghanistan, and then there are even some that are not recognised by the current regime, so you may even get a Visa but it wont be accepted when you get to the country.
Crossing from Aghanistan through the Wakhan corridor into China is not an option from any of the information I could find.
With the recent arrest of two british bikers (reasons aside) in Iran and the difficulty of getting a visa for Turkmenistan i made the choice to go through Russia. A transit visa for Russia can be gotten quite easily in Georgia (e visa does not work if you want to cross into Kazakhstan).
Another option is taking your bike from Georgia to Azerbaijan and then taking the ferry to Kazakhstan. This is definitely possible but certainly more expensive and time consuming than going through Russia.
Crossing China is obviously no issue, though expensive and you also need to plan in advance. Unfortunately the southwestern route is closed to foreigners apparently, so a longer tour is needed going northeast past the Gobi desert and then back south to Nepal.
I haven't come across any tours crossing China from Pakistan to Nepal, but maybe that's an option, though it would probably not be any faster/cheaper with the southern road closed to foreigners.
Concerning your thoughts on taking a ferry from the Arabian peninsula to Iran or India or something. Ive looked into this. Besides not helping with the India/Pakistan border situation it seems there is no ferries. There are many news articles describing the wishes and plans of several countries to start such a ferry service, but after searching for specifics I always came across the same info: there is no such ferry service at this moment.
I recommend you check out caravanistan forum, there's a lot of good info there. Hope i don't step on anyone's toes by mentioning this, but this forum has unfortunately become quite dead in recent times. I have heard many bikers saying that the facebook hubb group is very active though. Cant speak to it myself because I don't have facebook.
I hope this helps you. Maybe ill see you on the road.
Marc