Most big UK companies have employees north and south of the Border. Potentially, every cross-Border scheme will have to be divided. The Scottish part could be in a different currency, with different tax relief and regulations. Payrolls will have to be adjusted. All this pushes up costs exponentially, as would the requirement for a new regulator.
The Pension Protection Fund safety net, which was set up to operate in the UK, cannot be called upon to rescue failed schemes in another country.
Similarly, anyone with Isa savings and other tax breaks should consider that those are offered by the UK government to its own nationals and according to UK tax law. These cannot exist in a foreign country, as Scotland would become after independence.