One of my previous employers (small company) used QuickBooks via a permanent license. We paid for our small accounts (2x part timers) team to be trained to use the software and it worked well for us. Until QB decided to make the new version a subscription only model if we wanted to submit our VAT return digitally as required by HMRC. At this point we looked at the possiblity of the subscription model, but to get what we needed was about £300 per year and the cost of having our accounts team trained on the new version (different interface, new filters, reports and additional functionality). This added another £3,000 to the initial cost. We didn't upgrade and instead chose to pay £30 per year for a package to do our VAT digital uploads via a spreadsheet generated from our version of QB.
In this case, SAP are obviously having a Windows 8 / Office 365 moment. Pi55 your customers off with a completely different interface and charge a subscription for the software that you've been relatively happy with and familiar with using for years. Waste your clients' time learning a whole new interface and rely on someone else's data centre keeping your accounts safe. Then doubtless the new version will need to be customised (is there any SAP implementation that isn't?) at additional cost and then you can charge extra for that too.
Winner!