Ah ok. I'm an interested in this as a topic and would like to take a stab at this as I think it's an almost impossible project. I would like to caveat any opinion first by saying these: I have a great deal of experience customizing and creating little bits of bespoke functionality for various ERP systems (SAP obviously but also some of the smaller ones aimed at niche markets eg construction). I also have similar experience with similarly complicated and sprawling PLM systems. I've spent basically my entire software career around ERP and PLM systems and systems that break out pieces of ERP functionality and try to often do it elsewhere (usually badly), and then usually have to somehow bring everything back into an ERP system anyway, either manually or with at least some level of (but rarely complete) automation.
I am a CS graduate from a 'famous' UK university (UCL). I'm also a qualified CAD engineer, project manager within agile (DSDM agile etc)...ITIL qualified etc. i.e I've spent a lot of time across these kinds of many tentacled systems that really do reach across the entirety of any large business. I've worked with these systems from FTSE 50 businesses to small 50 person manufacturing startups.
I've also been involved in the migration between PLM systems (horrible from a data perspective - all those CAD files etc) and also ERP systems (horrible but largely just the mapping between two different Entity Relationship Diagrams almost incomprehensible to any living human in terms of complexity).
It would be an incredibly ambitious undertaking to compete with one of the major players in either of these spaces. It is not something you could really even do at the scale of a start-up the likes of which YC and the media understand as 'start-up'. You would need so many not just 'early stage' founders with wildly different skillsets, you would need effectively an entire large manufacturing business, from end to end, in terms of personnel because your 'domain expert' essentially includes 'every business function you can imagine'. That's before you could even begin to think about software. It's a fascinating idea but think about it - procurement/purchasing, warehousing and logistics, engineering and design, sales and marketing, finance (very important here), HR, operations, R&D, Q&A...and these are just the ones I can think of that I have come across in my dealings with these systems. They really do touch every department.
The length of time to market would also be such that this kind of project would not really be appropriate to describe as a 'start up'. You'd essentially be creating a 'Unicorn Killer' and that unicorn killer would need insane resources to even have a chance at market success. The number and requirement for specialist migration tools into your new system from existing clients would be a 'massive' undertaking also.
It's such a bold idea but I think to describe an undertaking of that size 'start-up' would be to completely stretch the meaning of the term 'start-up' so far beyond its usage that the term would lose all meaning.