To me that says a lot about the future of this company.
I find this confusing since with kit sales all you need to do is order some things and gather parts to complete a sale. The in house machined parts can be made along with turnkey parts. Make 9 instead of 6, need a part for a turn key ... make a couple more for inventory and kit sales that have already been paid for. The CNC parts can be cut while working on a turn key mill.
If volume exceeds capacity then it is time to add another mill to the production line.
To anyone waiting longer than 90 days, for parts for a kit that they paid for, I recommend they contact their credit card company and the Attorney General for the State of Connecticut. Continuing to take orders that will get filled "someday" is tantamount to fraud. Credit card rules require shipment within a certain time frame. He will be out of business very quickly if he cannot accept credit cards. He may just need a wake up call to get his act together and fulfill the orders that have been paid for and to ship as promised.
I know of several companies that have as much as a 2 year backlog that both tell you up front and don't take a dime until they are about ready to ship. They have a waiting list and will contact you periodically to verify your interest and will notify you of any change in the schedule. When for example people in front of you cancel and your order is pushed forward. They will also move your name back in the list if you have a temporary financial hardship. These are products costing $5,000 to $10,000
If it were me, I would accept a reasonable deposit no sooner than 4 weeks from the date of shipment and then make sure I shipped on time. If a problem arises communication is key. Calling the customer and explaining the problem goes a long way towards maintaining good customer relations. Prompt refunds on request and suspending new orders until the schedule is back on track are essential.
The absolute worst thing you can do is take new orders and sell parts to them as a turnkey mill when kit buyers wait months and months and months.