I run an online store using Magento CE 18.104.22.168. For all 25,000 items, the shipping is via UPS or USPS in the United States, based on weight. I do not use table rate or any other type of shipping - it's all weight based.
I would like the ability, one SKU at a time, for a product to be offered at a flat rate shipping amount. So if a cart has one item, and I have set flat rate shipping for that one item, that would appear as a shipping option along with the weight options. If a cart has 2+ items, then this logic doesn't apply, it's still the usual weight based shipping.
Ideally, I would create an attribute called flat_rate_usps which would be NULL. If I ever put a value in that field, then that would appear to my Magento customer as the $ amount which they could pay for USPS shipping.
So, it's an attribute (which I can do), set the data for that attribute for some SKUs (which I would do), and then the code in PHP in Magento which makes use of this field to (1) present the shipping option, and (2) if selected, pass the data correctly to the model for saving in the database and being part of the order.
If you have experience with Magento shipping, and you can solve this problem easily, then apply for the job. I know which PHP files to start out in - I want to hire someone who can actually write the code. This should be a half day job, I would imagine, for the person who has worked in the Magento shipping code before.
Email me with any questions.