The 16 bit memory bus and 10MB RAM limit (LC and Classic) were almost certainly marketing decisions. Here are some UK education prices for Macs in their lowest spec:
LC I 2/40: £1065; IIsi 2/40: £1606.50; IIci 5/40: £2726.50; IIfx 4/floppy: £2927
Classic I 1/floppy: £490; SE/30 2/40: £1556.75
Third party developers had previously used bits from the Plus and SE (even just ROMs) for creations such as MacColby, Dynamac, Intellitec MX Plus, Outbound (and a few more). The LC and Classic families therefore needed to be functionally limited to discourage third party developers.
Let's imagine how an LC I with a 32 bit RAM bus and no RAM limit might have been developed. Buy an LC I for £1065. Remove logic board and floppy disk from case. Throw away case and sell RAM, PSU and hard disk as spares. Install logic board into new large case with better PSU and cooling. Insert 68030 accelerator board with 8/16/24 bit graphics card (different VRAM sizes and ROMs for different resolutions) into PDS slot. Provide a PDS pass through slot for a network adapter (Ethernet or Token Ring) or for any other purpose. Encourage other manufacturers to make PDS cards with a pass through slot. Install RAM and hard disk at what ever size you like.
This monster could not use NuBus cards, but it would have hurt IIsi and IIci sales if it had been permitted to exist. The price difference between LC I and IIci was £1661.50 (say, £1800 after selling off the surplus LC I parts). There would have been so many opportunities to build something weird and wacky when the 68040 went into production.
LC I 2/40: £1065; IIsi 2/40: £1606.50; IIci 5/40: £2726.50; IIfx 4/floppy: £2927
Classic I 1/floppy: £490; SE/30 2/40: £1556.75
Third party developers had previously used bits from the Plus and SE (even just ROMs) for creations such as MacColby, Dynamac, Intellitec MX Plus, Outbound (and a few more). The LC and Classic families therefore needed to be functionally limited to discourage third party developers.
Let's imagine how an LC I with a 32 bit RAM bus and no RAM limit might have been developed. Buy an LC I for £1065. Remove logic board and floppy disk from case. Throw away case and sell RAM, PSU and hard disk as spares. Install logic board into new large case with better PSU and cooling. Insert 68030 accelerator board with 8/16/24 bit graphics card (different VRAM sizes and ROMs for different resolutions) into PDS slot. Provide a PDS pass through slot for a network adapter (Ethernet or Token Ring) or for any other purpose. Encourage other manufacturers to make PDS cards with a pass through slot. Install RAM and hard disk at what ever size you like.
This monster could not use NuBus cards, but it would have hurt IIsi and IIci sales if it had been permitted to exist. The price difference between LC I and IIci was £1661.50 (say, £1800 after selling off the surplus LC I parts). There would have been so many opportunities to build something weird and wacky when the 68040 went into production.