I think you need to ask to see the progress reports for prior years as well as the SDI that has been provided to the student. It sounds like the remedial intervention through the IEP they have had for 8 years hasn't been helping.
When was the student identified as needing help with reading? What level were they at back then? How much progress have they made? Do they have an intellectual disability that prevents them from being receptive to the special instruction in reading that has been provided? What has the school been doing? What are the teacher's certifications and/or qualifications to provide remedial reading services?
It's great that they are changing the SDI in the IEP given that is sounds like they have not responded well to prior intervention. I would ask to see the evidence/research on this push-in protocol and how it will do a better job with closing the gap between this child's present levels and where classmates are. Given how far behind they are, the school needs to be doing something different/better to catch this student up.
With the bullying that goes on in the MS grades, I would hesitate to do push-in IEP services. It could cause this student to become a target where they will start having mental health issues from the bullying in addition to the SLD.
In your shoes, I would also look at how the school is accommodating the student's deficit areas with things like talk to text software and audiobooks. If these are not in place, they will not have access to general education material.
My gut says that a child who is 6 years behind needs to be placed in a private special education school at public expense because it seems like the school has tried and failed this student. They need to start making 2 years of progress in reading each year so they can be caught up by the time they graduate. Given what the school wants to do, my feeling is that this student will drop out and never graduate. They will not be able to hold very many jobs with reading at this low a level given how important reading is. Would they even be able to fill out a job application if they don't start making better progress?