How complicated will it be to add a customer attribute in shopping cart rule condition in action section just like it shows product attribute list which are set as yes for using in promotional rule condition, Any ideas to start with will be much appreciated!
In Magento 2 (Community Edition), the only customer attributes you can use in a shopping cart price rule (using the default Magento functionality) are: - Shipping Postcode - Shipping Region - Shipping State / Province - Shipping Country
With that, you can create special offers for someone in just a state (i.e. Colorado), or a country (i.e. Canada), or just a specific postcode - this could be helpful if you wanted to do a local offer for in-store pickup in the 80303 zip code, for example.
Based on customer segments, you have the ability to do quite a bit of targeting, including total lifetime purchases, recency of purchases, categories of past purchases and lots of other great stuff.
I don't know if there's an extenion that will replicate this same functionality on the community platform at this point, but if you're looking for this specific functionality, the Enterprise platform might be a good fit.