Cost Segregation and 1031 Exchange Question

I have a two part question and would appreciate any guidance:

(1) Taxpayer does a 1031 exchange and defers $4,000,000 of gain. The replacement property was purchased for $10,000,000 and has the $4,000,000 basis reduction which gives it a tax basis of $6,000,000. Taxpayer subsequently gets a cost segregation study completed. Cost segregation breaks out the $10,000,000 between $6,000,000 of 1250 property and $4,000,000 of 1245 property (which is eligible for bonus/accelerated depreciation). Given that the taxpayer only has $6,000,000 of actual basis, what is the proper way to handle the results of the cost segregation study? Should the $6,000,000 book basis asset be pro-rated accordingly so that 40% of the basis ($4,000,000/$10,000,000) could qualify for bonus depreciation? Or does the $6,000,000 book basis stay entirely as 1250 property?

(2) If/when this property sales (or any property that has had a cost segregation study completed regardless of whether it was part of 1031 exchange or not), is there guidance on how to allocate the purchase price of the real estate between 1250 property and 1245 property that had been previously fully depreciated?

Thanks.

(1) The taxpayer only gets bonus on the excess basis as defined in Reg section 1.168(i)-6(b)(8). There's an example in the proposed bonus regs that shows how it works (for personal property under the pre-TCJA rules):

In November 2017, AA Corporation purchases a used drill press costing $ 10,000 and is granted a trade-in allowance of $ 2,000 on its old drill press. The used drill press is qualified property under section 168(k)(2)(A)(i). The old drill press had a basis of $ 1,200. Under sections 1012 and 1031(d), the basis of the used drill press is $ 9,200 ($ 1,200 basis of old drill press plus cash expended of $ 8,000). Only $ 8,000 of the basis of the used drill press satisfies the requirements of section 179(d)(3) and § 1.179-4(d) and, thus, satisfies the used property acquisition requirement of paragraph (b)(3)(iii) of this section. The remaining $ 1,200 of the basis of the used drill press does not satisfy the requirements of section 179(d)(3) and § 1.179-4(d) because it is determined by reference to the old drill press. Accordingly, assuming all other requirements are met, only $ 8,000 of the basis of the used drill press is eligible for the additional first year depreciation deduction.

(2) Section 1.1245-1(a)(5) has these rules. I will excerpt them for our convenience.

(5) In case of a sale, exchange, or involuntary conversion of section 1245 and non-section 1245 property in one transaction, the total amount realized upon the disposition shall be allocated between the section 1245 property and the non-section 1245 property in proportion to their respective fair market values. In general, if a buyer and seller have adverse interests as to the allocation of the amount realized between the section 1245 property and the non-section 1245 property, any arm's length agreement between the buyer and the seller will establish the allocation. In the absence of such an agreement, the allocation shall be made by taking into account the appropriate facts and circumstances. Some of the facts and circumstances which shall be taken into account to the extent appropriate include, but are not limited to, a comparison between the section 1245 property and all the property disposed of in such transaction of (i) the original cost and reproduction cost of construction, erection, or production, (ii) the remaining economic useful life, (iii) state of obsolescence, and (iv) anticipated expenditures to maintain, renovate, or to modernize.