The use of special uncial typeface to indicate quotations from the Old Testament would have been quite helpful and appropriate in the W&H Greek text of the Kingdom Interlinear Translations. However, I don't think that the reason that custom was not followed was to hide the fact that certain scriptures were quotations from the O.T. and that LORD appears in them.
If we consider the four examples that you gave we will see that not only does the NWT show they are quotations but also gives marginal reference where they come from.
2Th 1:9 ??from before the L ORD and from the glory of his strength, at the time he comes??
The 1950 edition of NWT has a marginal note on this verse : "Isa 2:21 LXX"
The 1984 Reference NWT has a marginal note on this verse : "Isa 2:21 ftn, LXX".
The footnote to Isa 2:21 (in the 1984 Reference NWT) reads :
"From before the fear of the Lord [Gr., Kyriou], and from the glory of his strength," LXX. [The Hebrew literally means "the splendor of his superiority".] Compare 2Th 1:9.
He 1:10 (the Father to the Son) ?You, at the beginning, O L ORD , laid the foundations??
This passage is clearly a quotation as he contrasts what was said about the angels, and what was said about the Son. All the editions of the NWT (and KIT) show this as a quotation by enclosing it within quotation marks.
In both the 1950 edition of NWT and the 1984 Reference NWT it has a marginal note on this verse : "Ps 102:25"
The 1984 Reference NWT has a marginal note on Ps 102:25 : "Ps 8:3; Ps 8:6; Heb 1:10".
1P 2:3 (speaking of the rejected Stone) ?you have tasted that the L
ORD is kind.?
The 1950 edition of NWT has a marginal note on this verse : "Ps 34:8"
The 1984 Reference NWT has a marginal note on this verse : "Ps 34:8". It also has a footnote which reads :
"The Lord." Gr., ho Kyrios. In a comment on this vs F. J. A. Hort wrote in The First Epistle of St Peter, London, 1898, p.104: "In the Psalm [34:8] ho kyrios stands for Jehovah, as it very often does, the LXX inserting and omitting the article with kurios on no apparent principle. On the other hand the next verse shews St Peter to have used ho kurios in its commonest though not universal N.T. sense, of Christ. It would be rash however to conclude that he meant to identify Jehovah with Christ. No such identification can be clearly made out in the N.T. St Peter is not here making a formal quotation, but merely borrowing O.T. language, and applying it in his own manner. His use, though different from that of the Psalm, is not at variance with it, for it is through the khrestotes ["kindness"] of the Son that the khrestotes of the Father is clearly made known to Christians: 'he that hath seen me hath seen the Father.' "
The 1984 Reference NWT has a marginal note on Ps 34:8 : "Jer 31:14; 1 Pe 2:3"
1P 3:15 ?But the L ORD (who is Christ) you must sanctify??
The 1950 edition of NWT has a footnote on the word LORD in this verse :
Sanctify the Christ as Lord, [Aleph]BAVgSyp; sanctify the Messiah our Lord, J 18 ; sanctify the Lord God, Textus Receptus; sanctify Jehovah God, J 7,8,12-14,16,17 .
The 1984 Reference NWT has a similar footnote on the word LORD :
"The Christ as Lord," [Aleph]ABC; TR, "the Lord God"; J 7,8,11-14,16,17,24 , "Jehovah God."
So, when you say regarding these verses, "The W&H text makes it clear that these are OT quotations and that L ORD appears in them. If the average JW were to discover this, what might happen?", it beggars the fact that in three of the four examples the NWT makes it clear these are OT references, and in the fourth reference it clearly shows that some manuscripts and Hebrew translations apply this 'LORD' to God/Jehovah. The only reason it is a surprise to some that NT writers quoted OT passages pertaining to Jehovah, and applied them to Jesus, is that they didn't bother to check the marginal references. It is common practice to identify God's prophets, angels and Son with Jehovah himself as he carries out his purpose vicariously. I doubt this would trouble any unitarian today anymore than it troubled the unitarian Christians in the early Church.
Having established that there was no attempt to hide these quotations in the NWT, the question still remains why the Greek text in KIT didn't follow the pattern in W&H of using a special uncial typeface for these passages. The probable reason to my mind is that the use of a different typeface is exegetical, not textual (i.e. based on the ancient manuscripts which were uncial throughout), and when you start confusing text and interpretation then you end up having 'Jehovah' in the NT and other anomalies.