A distribution from a traditional account in a 403(b) plan is permitted to be rolled over to a Roth IRA without going through a traditional IRA. You can do it either indirectly (which requires the 403(b) plan to withhold a minimum of 20% of the taxable amount for taxes) by direct rollover (no withholding required). You are also permitted to split the rollover with the taxable portion going to a traditional IRA and the nontaxable portion going to the Roth IRA. If done by direct rollover, the plan needs to make the payments directly to the traditional and Roth IRA accounts for your benefit. This means that they will know how much is being rolled over to each type of IRA so that they can prepare the code G Form 1099-R properly. See IRS Notice 2014-54: https://www.irs.gov/pub/irs-drop/n-14-54.pdf
There have been no recent tax law changes with regard to the pro-rata calculation of the taxable amount of distributions from a traditional IRA. The most recent relative change in the tax code was in 2008 when the tax code change to allow rollovers from traditional accounts in qualified retirement plans and in 2010 when the IRS made it mandatory for a plan to allow a such a rollover to be done by direct rollover.
